Damn. Zeroing out a 250GB drive shouldn't take 20 hours. A few hours maybe, but not 20. (Assuming 30MBps write speed, 2.315 hours in fact. Even if it was writing then reading it, which just a zero wipe shouldn't, maybe 5 hours.)
PowerMax (part of MaxBlast) does include a "quick" low-level format that just wipes the first and last 100MB or so, takes only a few minutes. That should of course wipe out the partition table and MBR.