Internet Sharing with USB Modem

I have a USB/flashdrive modem from my ISP, that is compatible only with WinXP. So I have it running on my XP laptop.
There are 2 other laptop users in my flat, each using windows 7 and Ubuntu 10.04.
We have a Linksys WRT54G wireless router.

Is it possible to connect the 2 other wireless laptops (Windows7 & Ubuntu 10.04) to the internet via the wireless router, whilst having the USB internet modem hosted from my WinXP laptop?

If so, how do I got about it?