From the "might just be crazy enough to work" department...
You could get VNC Viewer for PPC
(
http://www.cs.utah.edu/~midgley/wince/vnc.html), and run a VNC server
(
www.realvnc.com) on a PC attached to the same wireless network. I do
this with my wife's Axim X3i and it works like a champ. It can be a
bit slow (802.11b is not exactly optimal for pushing screen caps in
real time), but it gets the job done. The app would run on the PC's
processor, but input/output goes through the PPC.
Of course, the *sane* thing to do would be, as Brad says, to port the
app to Windows Mobile. If you're an MSDN dev, you should already have
access to embedded VC++, though of course that assumes that you
actually *wrote* the app, or at least have source. If all you can get
is the Win32 binary... well, see above. Put quite simply, a Win32
binary will never run on the x50 unless some very enterprising
individual makes a Win32 emulator for XScale. That's not a project I
intend to undertake anytime soon.