Get Windows 7 machine to connect to Win XP/Samba home network

I bought a Windows 7 laptop last year with the hope that it would connect to my existing network consisting of an XP machine and a server running Ubuntu Linux (with the sole aim of sharing files between the three machines). However, the Windows 7 machine won't even 'see' the other two machines. It is connected to the Internet via the same router as the others and will ping them both).
I have tried a few tutorials but without success so I think perhaps it needs someone to connect in remotely and investigate.
Hopefully this won't take too long for somebody that knows what they're doing but I am happy to pay for an hours work to get this sorted, otherwise I'll waste countless more hours trying to figure it out myself!