Poor NT Server Performance

I have a problem where DOS and some Windows based applications are performing poorly when run from Windows NT Server 4.0/SP6a.

The applications are written in house in either Clipper (DOS), or Visual FoxPro/ProMatrix (Windows). They are structured so that the individual records in the databases are small files, instead of one large database file.

What is noticeable is that before we migrated to a switched network comprising of Cisco Catalyst 4000 switches running at 100MBps servers and10Mbps desktops, everything appeared to run smoothly!.

Any ideas??