FoxPro 2.x for DOS under Windows XP -- turn off FoxPro's on screen clock, make the use look on the XP toolbar. Add as much memory as they will tolerate -- you can start XP with 128megs but with 110 open tables in your app, you should have as much memory as possible. Put the FOXxxxx.ESx files in the same directory with your applications EXE.

Without any further knowledge of your app, those are the points which come to mind -- I aid in supporting about 150 XP PC's running 2.6 code, VFP code, JAVA, and Microsoft's own Office programs. At one site there are about 30 PC's which run 2.6 all day everyday.