Windows 7

I have spent 4 or 5 hours trying to get Win 7 to connect to my home network. I have renamed and rebooted workgroups at length and eventually XP will see Win 7 but not vice versa. XP cannot see any shared folders on Win 7 as network sharing does not appear to be an option. Homegroup is a great idea but seems only to work with other Win 7 computers. Connect to work network does not work, even when I changed group names to workgroup, mshome, or homegroup. I don't run Vista but have set up networks for 98, 2000, Ubuntu, OSx and XP home and Pro - no problems. Anyone who can assist? I am sure I have overlooked the bl**** obvious, and yes - both computers and the sitecom 8 port switch were switched on! Win 7 goes through the switch to my router at the same time as XP without a problem, printer sharing does not work either.