@winlose it can be done. You need to setup a networking over USB cable such that PC can go to Internet via N900 by tethering. I am on the move now so I can't walk you thru right now. You may refer to the following link for some background:

http://wiki.maemo.org/N900_USB_networking

Or you may use bluetooth PAN(http://talk.maemo.org/showthread.php?t=58570), provided that your PC has bluetooth.