My xmas present??

Hijust after xmas this year im goin to upgrade to an ATHLON64 dual core.at the same time i going to need some memory and a motherboardhere we go then??1 is it worth upgrading to the dual core athlon's???2 what's the best memory..i'm using 1gb of ballistix memory, and it doesn't like athlon cpu's.i have to run it at 333mhz instead of 400,otherwise it starts CTD's..3 a good dual core mobo???4 vid card.i got powercolor x8oo pe 256mb.do i need to upgrade this??all suggestions are appreciated thanks steve