Yep, Apple uses the 802.11g wireless standard. My brother has an iBook and bought a Linksys Router (WRT45G, I think) to give him wireless access to the internet in his house. Works like a charm.
For the RAM, you can almost definitely get some cheaper elsewhere, although it probably can't be the cheap generic stuff. Macs tend to be picky with the RAM they accept. You may end up buying from Crucial, who I think are the ones Apple buys from, but it would still be cheaper than buying straight from Apple.
goates