1GB RAM should be enough now, the main thing you need to upgrade is your CPU, i'd be looking at getting at least a Core 2 Duo 2.66 GHz, if I were you i'd go the whole hog and get the Q6600, i've got the QX6700, and it works beautifully with Vista.
As for a graphics card, don't get an 8600GT, i'd recommend getting at least an 8600GTS 512MB off www.mwave.com.au, I paid $230 for mine to use for my backup PC.
Quote: "I cannot take these back can I?"
If it's still in its packaging you may be able to, if you've already installed the RAM, maybe if you're lucky, but if the CPU is already installed, no, since it'd be covered in paste.
Good luck with building your PC!