To clarify some stuff...
If you want to play wirelessly, meaning that you want to use either a wireless desktop (as uncommon as it seems) or a wireless laptop, you will require the XBOX to have a wireless ethernet bridge attached to it's ethernet port (the Linksys WET11 does this job perfectly)
If you want to play with wired ethernet cables, your XBOX needs to be wired to any router, and your PC / laptop needs to be wired too.
I understand what you mean now. Running XLink from teh PC (if you intend for it to be wired) will be just fine

Running XLink from the wireless laptop will not be fine heh, but if you still want to use the laptop, you can use the ethernet port on the laptop (most new laptops have them inbuilt) and you can get on XLink that way...
My VAIO is wireless for 98% of the time. The XBOX is hardwired to the router. I can still FTP to the XBOX over wireless connection or wired, but I get better speeds over wired obviously. If I want to play a game on XLink, I have to put my laptop on my desk next to my ethernet sockets in the wall and connect myself up to the router. I could get a wireless ethernet bridge, but I don't want to spend the money on it and I'd rather have my local area network running at 100mbps (even though I'll never get that much

) than 11mbps (I'm running on 802.11b). Plus the XBOX is right next to my TV which is on my desk which is next to my laptop which is next to the wired ethernet socket in the wall

make sense? hehe....