EIDE hard disks do not come with a SATA interface.
Your desktop may or may not have SATA connectors on it. In case you have a SATA hard disk in your laptop, but no SATA connector on your motherboard...then you can forget about using your laptop hard disk inside your desktop.
This is a real possibility, the SiS chipset is more often than not of low quality and low in features. And as you have a close to 10 year old PC, you might just be out of luck. Without the name/model of the motherboard in your PC I can't tell. Or it might be the same misery as I had here with such old motherboards (based on the Via chipset, one small step up from SiS). I couldn't install Windows XP on it's SATA ports without a floppy disk. Yes, I actually needed a working floppy, a floppy drive a cable to connect it to the motherboard, a CD/DVD player and a cable to connect it to the motherboard as well. Yes, those boards didn't have an option to boot from USB at all. Then I needed to start the installation procedure from the install CD and after a while it would ask for the floppy with a special driver on it that would make Windows recognize the SATA interface and when all went OK the installation continued.
SATA can be real "fun" on old computers. They gave the PC to you, perhaps not from the kindness of their hearts, but to prevent paying for this crap to throw it in a landfill. This is common in the Netherlands, You'll need to pay for throwing away electronics, you'll need to unload it into a special container where later on someone comes and takes those old consumer electronics apart, removes as much of the toxics as he/she can, throws the remainder into the landfill and recycles the toxics. I assume that there is something similar going on at municipalities in the UK too.
In the municipality where I lived that was actually quite expensive.
Anyway, if the same is true for your motherboard, good luck finding that special driver, a working floppy drive and a working floppy. You can't buy those new anymore, even here in Paraguay. Paraguay is a rather poor country, especially when you leave the cities. About 5 to 6 years ago I was asked to help someone out with preparing written off "clunkers" to be donated to charities for children. The amount of child mothers and single moms is very high, especially outside the cities. There are tribes of indians (Guarani) here where the boss of its elders makes any 11 or 12 year old girl a woman, because of their traditions. It's unprotected, so you can see those girls begging for money at traffic lights, baby in hand. It is also not unheard of that those girls get STDs and associated health problems from this tradition too.
Back to the topic: while I still had a lot of those laying around, it took hours before I had found a working combination of floppy drive and floppy to be able to install an operating system onto such systems. And, mind you, I had all of that hardware and the required software driver still in storage. If you don't...good luck.
10 to 11 years ago the transition to SATA started and not all motherboards were created equal around that time. Your PC is from that era and it uses a chipset that has a bad reputation. Now I'm hoping that your PC isn't plagued by all of this crap, but I am expecting it will be. Hardly worth spending any more time or money on than you already did.
You'd better start saving for a newer "clunker" that is based on a Intel Core 2 Duo CPU. These are much better equipped to handle the extra load that TOR requires and have no problem with Windows 7. And have motherboards that work much better with SATA devices and usually come with a 100/1000 MBit/sec onboard NIC. Those shouldn't be that expensive, as these are 9 to 10 years old.
For reference: I have a 8year old Core2 Duo CPU (2.6GHz) based motherboards (Asus) myself, it has 4GByte of RAM, 4 SATA2 connectors and about 1.5 years ago I put in a Samsung 840 EVO SSD hard disk in it. Even watching 1080p video that is encoded using the x265 video encoder works flawlessly. I also have a 1 year old PC with AMD APU 10 (APU stands for CPU and GPU combined and this one works at 4GHz). It has 8GByte of RAM and I can tell you that it is seriously faster than my old Core2 Duo PC.
I bought the PC case and all other parts for the Core2 Duo PC for 500 USD. Not including a mouse, keyboard and monitor, I easily spent 200 USD on a high quality mouse, keyboard and about 100 USD on a 19 inch monitor. After 5 years I did spent 50 USD on a good new power supply. Last year I bought a much better PC case and all other parts for the AMD APU 10 for 350 USD. Then I spent 150 USD on a 28 inch 1080p monitor and spent 50 USD on a decent enough mouse and keyboard. There was a power supply included with both PC cases, so there was no immediate need to buy separate ones. 750 USD for the old Core2 Duo PC in total, 550 USD for my new PC.
So if you are able to save 350 USD you can buy similar parts and have a much better PC (that won't even blink at the extra load of TOR). I think you can shave 75 to 100 USD off, if you go for a less powerful AMD APU (APU 8 or APU 6), buy a cheaper brand motherboard, less and/or slower RAM, smaller hard disk and PC case. Whatever you do, that new box will work fine with the monitor, mouse and keyboard you are using right now. There are many videos on the internet that show you how to build your own PC, step by step ('Linus tech tips' is a site with lots of videos on how to build PCs). The story above should make it clear that I can/do/want/need to build my own PC's.
As you already have a "zombie" PC (it should be dead, yet it lives) you have time to hunt for computer parts within your means. The reference above is just to indicate that you really don't need to spend that much on brand new PC hardware. People tend to charge a lot for second hand computer parts and if you keep score of what you have spent on those old computer parts to make your old clunker barely usable and what you would spend on brand new parts, the balance tips very quickly to getting brand new parts.
Keeping a modern PC up-to-date is also not that expensive. heck, a 60 USD SSD hard disk made my not-so-modern Core2 Duo PC practically a joy to use again.