Memory Match Really Necessary?

Any Hardware experts out there?

Just wondering how necessary the "matching" was the size of memory chips. I mean, if I buy a 1gb stick now (because I plan to buy a another one later) would keeping the 512 stick that is already in there THAT bad? Would I see no increase in speed with that extra 512 in there? Anyone know the clear answer on that?

you can but its not optimal.

Ram is Ram though, it would still be faster than your current config.

its like a 168 bucks for 2 gigs @ newegg.com

totally worth it.