upgrading memory

I was thinking of sticking in some more ram, I already have 512MB DDR RAM, does it matter what type of memory is already installed? Can I have different brands? I have been using some cad programs for work and reckon another 512 would help.

amd athlon xp 2400+
saphire radeon 9800 pro 128MB
SoundBlaster Audigy2 ZS Platinum 7.1
80GB Hard drive
19" HP f1904 TFT

Try get The same brand, you will have less problems

o ya stick with the same brand if the 2 sticks dont like eachother you will get restarts like a mo fo

Also, stick with the same kind of memory. So get another 512mb PC2100, or w/e type that might be.