The one successful Georgetown IM tournament that
I was at (and, probably not coincidentally, the
only one that I didn't run) was run one on night with
a round-robin, and people really seemed to enjoy
it. It works fine if you have a limited number of
teams - people don't have to make a huge commitment
over a number of weeks.
The only bad thing was
that it was held on a Thursday night in 1995 - Must
See TV probably eliminated a few potential teams.
MAKE ABSOLUTELY SURE that your tournament does not
conflict with the freshman geography test, the big game,
Survivor, or the big O-Town concert.