Need 512mb ram for my Dell Dimension 4100 Desktop with windows xp.

Dimension 4100 Memory Specifications
All u need, ...
Standard Memory 128 MB (removable)
Maximum Memory 512 MB
Memory Expansion 2 sockets
Memory Comments PC133 SDRAM DIMMs
CPU Type Intel Pentium III
Model Comments 133MHz FSB, Intel 815e chipset

U need 2 x 256MB sticks

Mushkin Enhanced Essentials 256MB 168-Pin SDRAM PC 133 Desktop Memory Model 990614
20-146-303-Z01