Desktop

Nothing that you can do before hand.
two good choices to get memory fro are Crucial or Kingston Technology will provide good tech support with buying generic memory sticks.right now you can get 128 between 40 to 50 bucks.
Ref:www.kingston.com

as soulrider said crucial and kingston are
your best bets for good RAM you might want to
consider just getting 256 since they are dirt
cheap now anyways

I agree that Crucial's and Kingston's reputations precede them, but I am also of the opinion that what matters most is that the RAM is compatible with your motherboard. Generic RAM--that is, RAM manufactured by several different companies--is oftenuniversally compatible. As SytemBoard stated, RAM is dirt cheap right now, anyway. But, to save a few more bucks, note the chipset used on your motherboard and then reference Pricewatch.com for RAM that is manufactured for that chipset.

As the two people answered above, Kingston is a good company for memory, but I have found that if you have a Compaq, HP, or Dell, it is best not to buy generic RAM but to buy the ones that they make.

All you need to ask for is PC100 ram. You may see ECC - which is error correcting and usually meant for servers - you don't really need this. By the way, Corsair makes excellent memory as well as the others mentioned, it's a bit on the pricey sidethough. Good luck.