Hi , i have a little problem here , i want to upgrade my pc with more memory but i dont no which one is the best or the correct one...

my pc conf is:

Vaio 1.30GHz Celeron
256mb PC-133 SDRAM

the problem is that there are many kinds of memorys and i dont know which one buy ... like i dont know if a DRR would be correct, i even know what is DRR o DRR2 also there ara another kind like the ones that have PC5300 PC2700 PC3200... i want to upgrade my pc with 512mb so ... i have a little troubles here....