Windows 7 Can Not See My XP Computer

There are numerous possibilities but check if the XP machine is accessible.
Go to the XP machine, open a command prompt and type ipconfig. Write down the ip address.

or

Get an ip-scanner and scan from the Win7 machine for the ip of the XP machine.

On Win7 pop up run and type the XP ip address eg. \\192.168.1.68 or whatever.

Continuing