Charles,
I took a look at the test harness source, and checked the API calls involved in the Platform SDK. I couldn't find anything involved that changed between 2K and XP. So, from a purely theorhetical POV, it should work. You said that it wasn't finding the VFP app, I've looked at the call to FindWindowEx and it should work, which is what I'm assuming the problem is. About all I can suggest is to step through the test harness in the debugger to see if you can locate what's failing.
George
Ubi caritas et amor, deus ibi est