Did you try compatibility mode? JK was originally designed for Windows 95 (but it works in 98SE and 2000 just fine for me).
JK Enhanced with the unofficial patch provided on the same network (jkhub.net) works for me. Of course I don't have XP, so I can't verify, but others have gotten it to work.
Anyway, try that first.
That reminds me, I need to try out that pack of addons somebody made to make some of the JKE objects more like the classic looks... the Bacta tanks with the "clip" on the side, the "clamp" over the stack of Mines, and the big medical cross symbol on the big health pack.