dtgreene: My level is so high that my THAC0 is 127.
Crosmando: ...
Yes, just a few levels ago I had -128 THAC0, and after casting the Dreamspell (which, among other things, lowers THAC0 by 20), my THAC0 was temporarily raised to 108. Now that I have gained those few levels, my THAC0 has permanently underflowed and I don't have to worry about the Dreamspell making it worse.
Just be warned: Hit me with a spell that penalizes my attack rolls and my attacks will become very accurate.
(In other words, I know that lower THAC0 is better; it just got so low that it underflowed.)
As a side note, in the DOS version of Bard's Tale 3 (which has so many bugs I can't recommend said version), a monk who levels up too high (past level 100) may find that her AC underflows and jumps to 138. If that happens, you should unequip the monk (to get her AC back into the negatives) and stop leveling her up.