I just removed mine to tighten and re-lube since it got loose and cruddy (see my previous post on my "downtube problems/failures".) It's a little better now, but the bearings are shot. So I measured and ordered a sealed cartridge bb. my DT VIII has a 115mm spindle length and standard english threaded 68mm size.
I ordered from harris cyclery
Shimano UN53 68x115mm axle
Qty: 1
Price: $24.95
Total: $24.95
you remove by first unthreading the lockring on the non-drive side. (counterclockwise and you don't have to take it all the way off; just a few turns.)
then you take an adjustable wrench to the same non-drive side cup and remove it entirely, again, counterclockwise. Mine was a little "sticky" coming off, but threaded back on nicely. this is all that's needed for cleaning, repacking and adjusting. replacement involves removing the fixed cup on the drive side. I am not looking forward to removal of the fixed cup (see the sheldon brown article Yan linked to)
At the same time, I also re-packed and re-lubed my headset because it was loaded with really poor grease.
good luck.
Last edited by Mr_Super_Socks; 03-09-06 at 10:50 AM.