A bluetooth adapter will normally work- I'm using a cheapo one I found off eBay with no problems on my eMac. This particular adapter isnt even meant to work on macs yet I use Romeo and iSynch no probs. Just plugged it in and it worked.
I'm guessing that a USB 801.11b/g adapter would work, but you might need drivers for it.
The USB 802.11b/g adapters are troublesome. Something to do with poor drivers. I would try to avoid them and go with an 802.11b/g to ethernet adapter I have heard that these work better.
And yes the bluetooth dongles seem to have no problems at all.