That is 2x the min. requirement so it should be fine for what you use your machine for. Worst case, if once you load up 10.5 it feels sluggish you buy more RAM. But I would give 10.5 a try before I bought more RAM.
Personally, I will install Leopard and try it out with 1GB at first.
Then if i really need it I will buy 2GB. But i do like to keep a lot of windows open at the same time, and Spaces will help me organize them, so i think i will have to buy more memory in the near future.