Go out and buy a cheap LinkSys router and replace the existing firmware on it with a different firmware (Can't think of it right now) and it turns it into an access point. Then, just place the router by the 360 and plug in the ethernet cable that came with the 360 to the router and the 360. Instant wireless adapter for less than $35.
We did that to get my brother out of the family room and off the big screen so we could actually watch T.V.
EDIT: It's called DD-WRT found Here
But in all seriousness, go for the video card.