Stuff written for Windows XP will not run on Windows Mobile. Which is why there are versions of Excel, Outlook, Word, etc. specifically called Pocket Excel, Pocket Outlook and so forth. In fact, until the last couple of years, you had be worried about if an application was written for your PROCESSOR. The early PocketPCs were built--depending on the OEM--on three different processors. Often you found an application written in three versions, one for each processor. Microsoft finally got tired of that mess and said all OEMs must use the ARM-based processors. I'm hoping they eventually do the same thing again and force OEMs to standardize even more so we can get our updated operating system INDEPENDENT of PDA manufacturer.
Anyway, the best you can hope for is to do a Google search for POCKETPC and INTERACTIVE KEY. I confess to not having a clue what an interactive key is, but I did a quick search and came up with this:
http://www.stingersplace.com/SLIKS/
Toward the bottom of the linked page is something about a demo version for PocketPC. They specifically mentioned it wasn't intended to be as full featured as Intkey. Perhaps this would be a good starting point, though.
The bottom line is you need to make sure software you're looking at is designed to run on ARM-based PocketPCs. Even better, you want it to have been written for Windows Mobile 2003. Most stuff written for PocketPC 2002 runs fine, and even most PocketPC 2000 works fine, too.
BTW, because I'm sure the question will come up, let me give you the Reader's Digest version of PocketPCs:
Microsoft has this ROM-based core operating platform called Windows CE. The actual operating system, graphical interface you're playing with on your X50v is Windows Mobile 2003, built on the WinCE 4.x platform. However, in the early days of these PDAs it was call PocketPC (often referred to now as PocketPC 2000). PPC2000 was built on the WinCE 2.x core. Then came PocketPC 2002, built on the WinCE 3.x core. Well, the actual devices were also called Pocket PC. This tended to be a bit confusing when you threw in the OEM. For instance, you had the Compaq iPaq Pocket PC running PocketPC 2002. So, MS decided to rename their operating system with the next generation of devices, so now you have PocketPCs running Windows Mobile operating system. The upcoming devices will be running Windows Mobile 2005, built on the WinCE 5.x core.
It's late and I'm sure I missed something, but this is the shorthand version anyway.