Hey I am running vista x64, it should run alright for you. 1GB ram might be a little small for vista though. I am running 2gb and the ram usage hovers around 50%. Vista uses the rest for cache (speeds up starting programs you use often).
I actually really enjoy using vista. Except for a few things (just the networking control panel section) it works perfectly. Even with the 64bit edition I only had to remove my 10 year old PCI ATI TV tuner due to lack of drivers.
If you want to be sure your computer runs fast, stick with XP (if you can find that disc).
There are ways you could test windows for 30 days before buying. If any of your friends have a vista cd just install it without a serial number (leave it blank) it will give you a 30 day trial of the OS. Then (provided you have installed the same version you wish to buy) you can simply buy the software, and plug in the key (activate it).
Good luck!
EDIT: I also just noticed, a 5700 nvidia card. I was running vista no problems (aero enabled) on a 128mb Geforce 5200.