You can use usb networking

Some info on the N900 setup:

http://wiki.maemo.org/N900_USB_networking

For the PC setup, this page is supposed to give information:

http://wiki.maemo.org/USB_networking..._Configuration

You don't mention what OS is on your PC, I guess it's probably XP.

I didn't see much there about windows XP. It looks a bit confusing. I don't have windows so I can't help much with that. Maybe it just works

On a PC running linux, it's not too hard. You have to have usbnet in the kernel, but this is normal, you just get the usbnet interface up, allow forwarding and set up the routes with the usual commands.

You need to have root access on the N900 to do the command to enable usbnet (ifup usb0)