Thanks Azzy64; that's useful info. Here's what I got (I have a dell by the way).
CPU: intel pentium 4 cpu 2.4ghz - core speed 2390mhz; fsb 132.9mhz; bus speed 532.6mhz
Cache: L1 kbytes, L2 512kbytes
Mainboard: chipset: intel i845PE
Graphic interface: agp ver 2.0, transfer rate 4x, max supported 4x, aperture size 128mbytes
Memory: DDR-Sdram 512mbytes Freq 166.1mhz, FSB DRAM 4:5...(rest probably not important)
SPD: slot 1 - DDR-SDRam 512mbytes, pc2700 (166mhz). Manuf: Infineon.
slot 2 - empty
So do I have to replace the one i have and get 2x512 or 1 gig or can i keep the one already in and get 512more? Also, why does it say ddr-sdram? I thought it's one or other?