Hmmm... I think it uses UE 3, but I'm not sure.
You positive on that?
Cause UE3 is for Unreal Tournament 3; UT3 runs on Unreal Engine 3, so it'd use UEd 3.
What he MEANT to say most likely is the game is for UT2003 or 2004 since they both run on UE2 (Minor note here, UT2004 actually uses UE2.5, but for most intents and purposes a ut2003 map should work on 2004 since 2004 is mostly a glorified upgrade to 2003).
To go with that both are likely using UnrealEd 2 or 2.5 to go with Unreal Engine 2 or 2.5
Thats evident by Postal 2 actually - Postal 2 uses the Unreal 2 engine as well. For the hell of it I tried modifying one of its maps with the editor that came with UT2003 - it loads it just fine. Didn't play in ut2003 cause it was missing the stuff designed for 2003 (spawn points, weapon spawns for 2003, etc), but it's the same editor for the same engine.
Short version: Editor is UEd 2/2.5, game is ut2003/2004, engine is Unreal 2.0/2.5. UE3 = UT2007 (officially Unreal Tournament 3, but I like using the year better), which uses UnrealEd 3. This isn't a 2007 map since the original poster referenced Ued 2k4, which sounds like they meant the editor that came with UT2004
I'd love to see the map at the very least, maybe it'll re-kindle some interest I had in map-making, and this system can't run UT3 (does pretty well with 2k4 though - always liked maps where stuff changes around every few minutes so the map itself is an opponent, not just the players on that map

)