you want to share files etc between PCs?
Firstly, I would disconnect any router etc from the Internet. Then I would disable all firewalls (including the Windows one). Have you made the workgroup name the same across all PCs? (Vista and XP have different default worgroup names). Have you set folders to be shared explicitly?
Vista has changed a lot in teh sharing space, best read the following article.
File and Printer Sharing in Windows Vista
To be brutally honest, this is another example of why I REALLY don't like Microsoft operating systems. In Linux you set up a samba share and job done.
One thing I would ask, why do all this spiders web of shares, teh most reliable and simplest solution is a Network attached storage device and all PCs use that as a repository for anything worth sharing. devices such as the Linksys 'slug' might be your best policy to sort out all your problems in one if you are 'techie' oriented (basically a replacement firmware for a linksys NAS unit that gives you effectively a mini PC to run file print etc serving. google unslung if you want more info)
and