Vista has some strange new security foibles that I haven't sorted out completely. On rumor (unconfirmed) is that it will refuse to admit the presence of other computers - and/or the inernet if other computers share the access - unless passwords are assigned to administrator account(s) and to at least one user account on the Vista machine. It is not clear (i.e. Microsoft doesn't comment) whether similar passwords are required for other machines on the shared connections. It appears that it may either share drives or connect, but not both, without the "proper" password/user assignments. Microsoft gives NO HELP.
In order for several "connected" computers to share the internet connection, the connection usually can be set up on one computer and the others will "discover it." This may not work if the Vista computer has already "found" other local computers. (Unconfirmed again, although I find lots of advertisements that say everything works automatically).
The recommendations I got for my wired (ethernet) LAN was to set up one computer to connect to the internet via the router and then connect all the others to the interent. After the internet connection was made one of the computers on the local network must "create a local network." Each of the other computers on the local network then needs to "join" the network.
Some wireless info indicates a reverse procedure, where the wireless network must be created before establishing the internet connection - but that was pre-Vista.
At present, all four of my computers can get on the internet and can receive email. One of the three WinXP computers can access shared drives on the other two WinXP computers, and sometimes can connect to the shared drive on the Vista. One other WinXP can see the other WinXP shared resources but NEVER the Vista. One of the WinXPs can't see anything but it's own dumb drive. The Vista can't connect to anything but the internet.
I'm on about page 80 (of 680) in my new O'Reilly manual, but making slow progress. Ask again in about a year - maybe - if I still have the Vista machine.