Hillrider was referring to "downtube" when he said "dt."
As long as the eight speed shifters are Shimano but not Shimano Dura Ace, any modern Shimano rear derailleur, excluding Dura Ace, will work in index mode. So the XT rear derailleur will work fine. Eight speed and earlier Dura Ace shifters/derailleurs are in their own little world when it comes to indexing.
Be sure and match the number of "speeds" in the shifters to the number of "speeds" on the cassette if you want to use the shifters in index mode.
Last edited by well biked; 12-17-07 at 10:05 PM.