I think I'm using the Velious UI... but go into whatever .xml file you have your XP bar on (mine's in the inventory window, so I am editing EQUI_Inventory.xml) and:
1) Create a BACKUP... label it EQUI_Inventory.bak for instance, so you can revert back to it if you F something up. Otherwise EQ may crash out when it tries to load your UI.
2) Look for lines that describe the XP gauge, like:
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and delete them.
3) Then you need to find the part where it defines all the pieces of the UI and remove the piece definition as well:
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4) Save the file as the actual EQUI_Inventory.xml file (or whatever file you were modifying) and enjoy worry-free XPing!
As an added challenge to the game, for pro clerics, remove the HP bars in your group's status window!!