if you want to use a nice desktop tool to run another virtual pc in a window and easily test software, virtualpc2005 and vmware workstation are the tools of choice (neither free).
I mostly use VMware workstation - not dirt cheap, but a nice bit of software. However, I think that VMware Player might fit the bill for the above if you're looking for a simple, free desktop VM. Just download (http://www.vmware.com/download/player/
) and install it, then to create a custom virtual machine, you can do one of the following:
1) download one of VMware's 'community Virtual machines' (http://www.vmware.co...ppliances/directory/
) that have specs (memory, disk size, etc.) how you want, then boot it from a bootable CD, format the virtual disk and install your test OS. See http://www.virtualiz...al-machine-with.html
2) go to http://www.easyvmx.com/
- this sites hosts a virtual machine creator. You plug in the parameters you want for a VM (again - memory, disk size, etc.) and it creates a set of VM files for you to download in a .zip. EasyVMX.com lets you configure nearly all possible VM parameters - for starting out, I suggest using the 'super easy' page which presents only the most important. Since the virtual disk is empty, the download is very small. Once again, boot the VM from an install CD, and you're gold!
Note that even though you're asked to select an OS for the VM, that only sets some default parameters - you will still need to install the OS for the VM (and have the proper licensing - it could get expensive with WinXP).
The nice thing about VMs is that they're easy to copy - set up a WinXP (or whatever) VM, copy it to a backup location, then use the VM for your tests. If and when it gets hosed, just delete it and copy the clean VM from the backup.
Also, even though VMWare player will allow you to run only one VM at a time, you can have as many VMs available to run as you have disk space for. Using VMs is easily the best way to check out open source operating systems if you don't have the spare hardware to use.
Oh, and thanks everyone for the greetings!