WinCE 3 is the embedded OS behind many of these small devices, such as pocketpc's, smartphones, and hpc's. PocketPC is the add-on for the OS that lets it work well with a specific device called a PocketPC (quarter VGA screens, arm processors, etc).
Stuff has to be ported, but there's ports of many big-name software titles, like Word (albeit pretty sad), excel, powerpoint clones, outlook (pim), acrobat reader, ACT, Quicken, expedia streets and trips, instant messangers etc.
But when you look around, there should be lots of software for many purposes, from multimedia to games to information management and productivity, internet, etc. 3D graphics would probably be a no go though, because the only 3d you'll find are in games such as Argentium (sp?). These devices probably aren't so fast, though I don't have a pocketpc 2002 model.
Yes, a tablet would work, but at ~$2000, a cheaper laptop would be a much better consideration.