[Leica] my camera bag is getting BIGGER! -- GPS advice

[kcassidy at asc.upenn.edu (Kyle Cassidy)]

okay -- for reasons that hopefully i'll be able to talk about in the
weeks ahead in more detail (though those of you who are shrewd will
probably figure it out without too much trouble), i'm driving across
america this summer stopping in various places to do a series of
portraits. i'm thinking that i might want to get a GPS to make
navigating between all these places easier (i'll be stopping in 16
cities and probably taking two, maybe three portraits in each). 
 
my thoughts:
 
1) i'd like a gps that interfaces with my laptop, since i'll be bringing
a laptop to store my, er, film, on. it's a mac g4.
 
2) after this trip i probably won't use the GPS for ANYTHING  except
geo caching snickers bars. -- i don't own a car.
 
so ... i'd like a handheld unit, it doesn't need intergal maps, but
interfacing to a laptop with mapping is essential. and since i'm not
going to use it much afterwards, cheap is good, used is good ....
renting might not be bad ....
 
any advice on what to get? 
 
kyle