You need a router and some network work cards (this can either be wired or Wireless).
Its simple to do- you plug the BB modem into your router and that your two PC's into the router.
This will let you share the connection.
They will sell you what you need at PCWORLD or if you happy online click here .
ebuyer sell there own brand router for £23.50 inc vat. click here
Network Cards:3.52 inc vat
Those are the cheapes I could find. You might however wish to go for a brand ie. Netgear!