You want a 184-pin PC3200 DIMM such as the Crucial CT25672Y40B. It's not going to be cheap: you're beyond the point where the price is rising because of rarity.
You should visit the Crucial web site (there are others): the site will be able to check your machine, and tell you what products work with it, taking into account any limitations specific to your motherboard. Not all DDR motherboards could take 2GB DIMMs, and some couldn't take double-sided DIMMs, etc.
Edit: I misread, thought you wanted 2GB units rather than 1GB. See Corsair Memory VS2GBKIT400C3 2 GB PC3200 400MHz 184-Pin DDR Desktop Memory Kit at