Also, search syscomments for procs or functions that may drop that table. I once had a long release script where I forgot the go between a alter proc and a drop table. The drop got compiled into my proc (in error) and it took me forever to figure out why that table kept getting dropped every night ...
If your database uses FULL Recovery model it would be possible to selective restore the database (e.g. to another, temporary, database) and see the point at which the table was dropped, but it won't tell you who did it - but other activity in the database at the time the table was dropped might help identify the culprit.
You could also try a log reader - from RedGate or Lumiscent(sp?)