If you consider that most in dash aftermarket nav systems are around the $2000 mark, a computer is a great idea; more capability for less money.
I recommend browsing through some of the sub-forums here for ideas, go to the search feature in the top right and look for cars like yours ('show off your project' is a good place for that), also spend some time in the FAQ emporium and newbie sub forums.
I came to this site originally to find out info on connecting my ipod to my aftermarket pioneer deck, then I found out what the site is really about, and I'm well underway to put the 'puter in. Maybe you'll be inspired too.
BTW: Pancit175:
In your sig, it says "Do it right or don't do it all" but then just slightly below that you mention you are considering redoing it... Wouldn't that mean you didn't do it right the first time?