Not all that complicated but there is a lot of different components working with each other. I am not sure I would run out and get new computers bases on the above. It's interesting that it happened when going from v4 to v5, which would make it fairly obvious it's some type of connection issue. This is over my head, so I hate making suggestions, although moving to SQL Workgroup couldn't hurt.
I still think you need to isolate and trouble shoot. Get a certain group of similar computers working without dropping SQL, then add on.
I know the difficult part for AC tech and it is also a frustration for them is it can be difficult for them to troubleshoot the issue when it is more of a networking issue than a v5 issue
Ultimately, you may need the services of someone who specializes in SQL Server databases and networking. There are many online and many who will provide remote service. I will try to get my SQL friend on Experts Exchange to take a peek in here.
