Do use non-ECC ram, everyone else does. ECC is for servers and critical equipment not desktop computers. If you want to make sure ram is not delivering wrong data then run Memtest86, http://www.memtest.org/
All new ram should be tested with this generic tool, recommended by most memory makers. No matter price you can never be sure ram is not faulty. If errors you simply send ram module back and will get a new. Result will not be questioned. A few things you have to be aware of with ram. Timings, what speed you set it to, must be correct. The voltage you tell motherboard to deliver must be correct. A 100% healthy module can give errors is setup is wrong. This should be done by shop, what you pay - but lets see...
Ram can be very picky to set up, the ram I have now only works well with 2.6v. 2.7v and it will fail. If motherboard overvolts a 2.6v setting what works could be 2.55 or 2.5v - even if "wrong". Makers happily say use 2.8! Lots of strange things can happen. With ram it is a very good idea to test properly, as with Memtest86. Give peace in mind. Ram errors are evil and can be hard to diagnose if not aware of this. Works perfect or must be replaced is all you have to go by.
I doubt that upgrade price to Vista. There will be several versions but the prices Ive seen up to now have been way above what you mention.
DirectX 10 eyecandy, games starting to make use of DX10 could make you interested in Vista. Have to buy new video card then, probably as another 1gb of memory too. All are in same boat. Was it not for the DX10 stuff I think Vista will take ages to become popular - most are happy with XP as it is. Windows 98 -> XP really meant something, now it is like you get/pay for something you dont even feel you need
If Vista really becomes so cheap upgrade cycle will be accelerated of course, I want to see price tag in an advertisement before I believe it