Other than direct transfer from a disc, your only option is going to be FTP.
The Xbox uses a file system (fatx), that windows does not recognize (or any other OS for that matter), so you can have the drive unlocked, and actually see it is there, but do nothing with it, other than format it to a compatible file system, which of course makes it useless for Xbox.
I was the one to recommend streaming, and I recommend it yet again. FTP'ing is going to require a network connection anyway, and unless you are only planning on putting a few things on the Xbox every now and then, then moving it to location for transfer is going to be a pain.
You don't have to buy the Xbox wireless adapter specifically. It is just a regular ethernet bridge, so any other would work just as well. A quick froogle search for
wireless ethernet bridge turned up some for much less than $100.
Here is a Linksys one at buy.com, from that search, for only $32.99.