When I had my problems with installing AC and the network, I found a bunch of things that can slow Win XP and Win 7 network connection speed. The following is based on the fact that your rebuild of the server is not *exactly* as before the rebuild, since you say that nothing on the XP computers were changed. Maybe the rebuild caused some discrepancy with the XP computers that weren't there before the rebuild on the Win 7 server.

You may now be subject to the "slow network transfers between Win XP and Win 7". There are a bunch of stuff on this if you Google this. Maybe one or more of the suggestions there will help.

One, which fixed my problem, is a registry key on Win XP that concerns the "task scheduler".

http://www.speedguide.net/articles/lan-tweaking-1607

I only did the "disable network task scheduler" stuff, since I found that in numerous Google search links. In my case, the first time browsing to a networked computer in network neighborhood took *many* seconds, where other computers doing the same thing took a second or less.

Of course, this assumes that the "change" in the Win 7 server is the cause that the Win XP now has problems. Hope something helps....