the problem is the game doesnt handle multiple processors (or virtual multiples like P4's with hyperthreading.) when using xp. so you just have to run jk2MP.exe in safe mode
1.02 works fine just run it in compatibility mode
C:\Program Files\LucasArts\Star Wars JK II Jedi Outcast\GameData\ jk2mp.exe
#1: Go to your jk2mp.exe
#2: Right click it and then click "properties" at the bottom
#3: Click the "Compatibility" tab
#4 Check the box that says "Run this program in Compatibility mode" and select Windows 98 from the dropdown box.
#5: Click "Apply" and "Ok" and then try running JK2MP again and see if it works.