'prespawn' for largemouth bass is generally(there are no absolutes in fishing!) when the water temp gets to about 50-55 degrees or so...
that being said, there are
always some fish shallow, no matter the time of year. In fact, you can catch a helluva lotta fish by just concentrating on 7 ft of water or less in any body of water. Doing so, you just eliminated ALOT of area, so it should make finding the fish-holding areas easier.
This weekend they're fishing the 2010 Basssmaster Classic in Alabama, catching most fish on lipless rattlebaits in 4-6 ft of water, and the water temp is high 40s, low 50s.
I'd have immediately thought "jigs in deeper water" or
maybe s-l-o-w rolling spinnerbaits, but hey, whatever it takes.
EDIT: GREAT info above from Mike ^^^
EDIT #2: a good tip for 'prespawn' is to find those spawning areas, then back up to the nearest drop-off or maybe just deeper offshore adjacent to those spawning areas.
**'deeper' is relative - if the whole area is only 3 feet deep, 5 feet is deeper