i think you had a typo, but you meant to say that it runs fine over a wired connection?

 

Assuming that the signal quality is good and that you've ruled out other factors, try a free program called cablenut (assuming you have XP).  Load the settings appropriate for your internet connection and OS.  It may take a little playing around with to get the best results.  You'll need to reset after any chances.

 

At anyrate, it worked for me and a bunch of others when wireless internet speeds were drastically lower than they should be (and wired worked fine).

nice ...   it's a great little program isn't it?   :D