hi im planning on upgrading my guest computers ram. currently the specs are: 1.3ghz AMD 128mb pc 133 sdram 250 watt psu 120 gb HD 128MB Nvidia DVD-RW DVD-ROM i was wondering if ddr means double data rate. then does that mean 1 512mb ddr ram. is about the same thing as 2 512mb pc133 sdrams? the most my guest computer can take is 1.5gb of pc133 sdram. im wondering if i need all 1.5gb or if i only need 1gb. i dont want only 512mb in it. my cpu is the most the board can handle. and i was wondering if my 250watt psu should be fine running the newer setup. with either 2 or 3 512mb sdrams.thanks..