Microsoft has a hotfix for the LLPT in Windows XP that will also make it so that windows 7 computer will see windows xp computers. KB922120-v6-x86 fix215806
Change setting "Allow Windows to manage homegroup connections (recommended)" to "Use user accounts and passwords to connect to other computers". This should let your windows 7 computer see all the computers on your home network regaurdless of the operating system. The setting is under Network...