Hi there
I personaly would get the ddr3 but maybe this would help you:
What is the Difference between DDR2 and DDR3 Memory?
as for the hdd if your not going to do some hardcore stuff, just get 2 wd raptors 10k in raid..
Well for overclocking it depends, do you want more power out of your hardware or going to run multiple apps at once? Does the apps need the extra boost?
For the warranty part not sure on I haven't RMA anything ( knock on wood )
Have you try out windows 7? It's not like vista I have it and it's like xp but better.. Give the beta a try..
I hope I helped you some way, once I know what you want I'll get you a list
Do you want c2d c2q or i7?