Welcome to AC Tommy.
I used to have a P2P system until Sept '07 I upgraded to server/client system.
My practice management program worked beautifully until I installed Vista on my "Main Computer." Then it kept crashing and not responding. Once I upgraded to server model, everything was fine.
I think given the configuration you described, I would DEFINITELY re-install Window XP-Pro on that one lingering machine w/ Vista. While in theory XP-Pro and Vista should interface, in practice they don't do so very well. there are many differences between the two. Either have EVERYTHING XP-PRO, or EVERYTHING VISTA. If you go w/ VISTA, make certain it is BUSINESS edition.
I love Bert like a brother, but I will disagree w/ him on this point. I don't consider Vista to XP-Pro a "downgrade." My bias is that you should have all your machines running Vista Business.
I am actually using Vista-Business on all of my clients and Window Small Business Server 2003 on my server. For a reasonably small investment, you could upgrade to have a real server and therefore a much more robust system.
P2P connections are prone to "hang-ups," and "broken links." This is probably the issue, however removing Vista or upgrading everything to Vista could resolve the issue.
Another point or two you MUST consider, as Al alluded to. Firewalls. Firewalls. Firewalls. They are great but the source of many a problem. Make certain that AC is on the "allowed list," on each computer's version of Window Firewall. Make certain that IF your virus scanner is ALSO a software firewall (like McAfee), you TURN OFF the software firewall.
The only firewalls you should have are your HARDWARE firewall that your internet modem connects to, and your Window Firewall on every machine. Any other SOFTWARE firewalls need to be off.
