Well to start with I wouldn't recommend "ripping out" anything
Personally I've never used Corsair but the name seems to get bandied about on the forum quite a bit; I couldn't tell you whether that is good or bad, maybe do a search and see what that comes up with?
Is the new RAM coming as 1 x 2GB stick or 2 x matched 1GB sticks?
I bought one 2gb stick, as I figured then I only have to buy one more 2gb stick if I need more memory. So shall I leave one 512mb stick in the computer? (= 2.5gb) or only have the 2gb?