Ok i need some help with my PC build

I want to build a pc for 500USD does not have to game hard just AOEII and WOW.

however I want to turn this baby into a server/htpc in the next couple of years so please keep that in mind.

i will be building my self and i could increase the budget if really needed.

Also dual core is nessary(or quad cuz it will eventualy be playing movies and acting as a server) and i already have a HDD with an OS on it.

And PSU needs to be 80%+

thx comunity :)'