It's difficult to tell. Personally, (and I am not looking at your network and don't doubt your IT person), but it is hard to say it is AC or it is the network. Obviously, like medicine, they all play together which is obvious since, unfortunately, you are having problems and a lot of us aren't.
I remember starting way back when -- I believe I was one of the first -- and our programs would crash with no warning about four to eight times per day. At that time, you HAD to run Amazing Utilities and ALL AC programs had to be shut down. Well, this was a nightmare given there was some type of leak and, even if AC did not appear to be running, it could be running in the background. You had to close it in task manager. To make matters worse, a couple of XP Programs in the back on a non-domain network had Fast User Switching. So, here we were, four to eight times a day, completely stopping with three or four of us running to each machine to make sure AC was not running, looking between the different users on the XP Pro faster user switching machines and finally going to the Amazing Utilities on the server and fixing the problem. Of course, a good many of those times, it would say AC was still running. So, someone's AC could crash in room 1, and you would be in room 6 and have no idea until your AC froze (they all crashed due to the first one) or you heard the alarm that everyone needed to get out of AC, while Bert manned the server and the nurses were running around turning the ACs off. The patients thought we were crazy, and my partner at the time who has NO patience was already switching to paper progress notes and writing out scripts on paper pads. AARRGGHH!! This went on for weeks with almost daily calls to Jon who told me that there were three practices like this. I have no idea how I continued to keep my impatient partner to hang in there. I tried everything and finally put an upgraded pro version of Access on the server (which, of course, should not have made a difference) and it never crashed again. So, see, it could be much worse.
Anyway, I think I would troubleshoot one thing at a time. I think you need to isolate as much as you can even though that is hard to do during office hours. How many doctors do you have? Can you work from less computers?
I would look at networking as it relates to the computers that are crashing the most. Look at the network cards. It is bad that 32-bit systems can only "see" around 3.2GB of the total RAM. That will all change with 64-bit computers. It sounds as though you have plenty of computing power and RAM.
You could download the .iso version of Memtest 86 at
http://www.memtest86.com/ and boot to it and check your RAM. Who knows. I had a friend do this on her computer, and she had a bad stick of RAM. I am assuming this is Vista Business? Not that Home shouldn't work, but that could be an issue.
I know that many times when I have issues with a computer, it can be the video card. Vista, as you know, tends to need a more powerful video card but generally only when you use Aero. If you are using that, turn it off. But, I just fixed this girl's computer by having her download a new driver for her video card. And, my HP server I had last year was out of commission for over ten days before the HP tech came out and figured out it was a bad video card (the monitor was still looking great).
Also, is anyone using the main computer? If so, is there is anyway to isolate that computer for awhile? This would be a great time to schedule 10 or 15 patients on a weekend and just use a few computers to see.
It can be frustrating, but it has to be a combination of AC code and your network not that anything is wrong with it. Have you downloaded a newer version or just reinstalled that one?
Maybe even download a program with SQL to your computer and play with it in isolation. If it works fine, make your computer the database computer.
Just some ideas. Good luck. Let me know if there is anything else I can do.
And, there is always the six-day free trial on Experts-Exchange where you could ask the question under Vista, XP Pro and Networking. They usually answer about 75% of my questions.
