Satellites seem to be a bit different to standard broadband.
There's a satellite FAQ and forum here that might help.
http://www.broadbandreports.com/faq/satellite
If you have a connection from the satellite into the XP desktop then normally you could enable ICS on the connection, connect another NIC to a wireless Access Point (or just use a wireless PCI card or USB) and put a wireless PC card in the laptop. I guess the simplest is a wireless USB on the desktop and a wireless PC card in the laprop and connect them in wireless peer-peer mode.
But its the ISP software that worries me.