One thing he might do to make this easier to pull is to install conduit bodies
at both ends of the underground part of the run to get short pull points. If
you do run 3 wires you are depending on the conduit as the grounding path or
you are setting up a 3 wire feeder and regrounding the neutral in the garage.
Both require driving a ground rod at the garage. (actually every scenario of a
sub panel does).

See this from the 2002 NEC handbook

http://members.aol.com/gfretwell/sub...g2subpanel.htm