Peachtree Very Slow Over a Network

Customer has Peachtree Manufacturing 2007 in a networked setup.

One of the machines that was also used by a worker holds the Peachtree data that the other computers access (via Windows file sharing).

Worked fine until two new machines were put on the network, one wireless (by adding an access point).  Only one of the new machines was set up with Peachtree, and this is via Virtual PC because Vista won't work with Peachtree Manufacturing 2007.

The clients using Peachtree have recently complained that Peachtree runs very slow.  Upon inspection, it takes a very long time to move through fields whilst creating invoices/sales orders, closing invoices takes a long time, exiting the program takes a long time and sometimes crashes, and it generally takes awhile to get fields to populate.  Sometimes it runs very fast with no problems, but then sometimes it runs slow to bring up new windows or new data.  Very weird.  The long time is from 5-10 seconds up to 30 seconds.

Tried everything on the machine holding the Peachtree data - removing unneeded software, turning off antivirus, nothing so far has given solid results.  Also tried unplugging the wireless router as that was the big material change to the network.  Nope.  Also, one of the hubs on the network was replaced for a switch, now everything is switched instead of being on a hub and a switch.

So, the software was installed on another machine (not used by anybody currently) and the data was moved there, and the paths on the client machines were changed to look there for the company data.  Now one of the networked clients (the one using the computer originally holding the data - yes, the path was changed to the new server so they're not accessing it from the hard drive) has no problems, things aren't slow anymore, and if anybody uses that server itself they won't have a problem because they're accessing the hard drive without going through the network, but two other clients are still having the performance issues noted above.

I tried turning off the Smart Data Entry options as outlined in the Sage support, and I tried everything else listed above.

I'm pulling my hair out trying to get this to work.  I wish they would switch to QuickBooks but they like the reporting capabilities of PT.

Any ideas?