I have mine set up as an ethernet cable from the xbox to my router, works fine. To access my pictures and music from my pc I also have an ethernet from router to pc. I agree about the astronomical cost of the wireless adaptor and so havent bought one.
As an aside, when I bought the xbox a few weeks ago I thought that the included xbox live silver memebership was enough for the chatting to other online players(for my son not me!). However, I have since found out I have to pay amonthly sub when the gold trial expires, grrrrr