There are a number of postings on that topic in this forum, if you do a little searching. Yes, you can put 1GB in. Yes, almost any 1GB DDR PC 2100 (or above) 200 pin SO-DIMM should work. Don't get DDR2 and don't get 184 pin (standard desktop-size modules). Otherwise, you're set.
I'd summarize the other threads as: don't go for the absolute cheapest RAM, get a decent brand from a reputable vendor with a reasonable return policy if possible. Generally Crucial, Corsair, Kingston and Samsung among others are well-regarded.
Potential candidate:
Crucial. Good pricing and some reviews:
Newegg.