Ok, I'll be the first to admit I have no idea what I'm talking about here,
so I'm turning to anyone who might know...

My wife is training for a half-marathon in September,
and I was thinking of getting her one of those GPS watches for her birthday.

From the little bit of research I've done, most models will track the path you ran
(...and will download the info to a computer ), but what I'm looking for
is a way to input the path you WANT to run, and have the GPS track your progress.
(ie. enter the path of the half-marathon, so that my wife can have a real-time
view of her pace and remaining distance.  Ie. she can track her progress
on the given map in real-time... )

I know car GPS systems will do this, but is there anything  
similar for watch/running GPS systems ?

Any info would be great.

Thanks,
Steph

maybe an iphone app?????

No idea about GPS, but there are some good map services (using Google Maps) to plot out courses, such as http://www.mapmyrun.com/search.

i bopught my wife the Garmin Forerunner 305 - with heart monitor

It does everything, she really loves it, i don't know about inputting a route, but apparently it's the best GPS watch out there, we found it cheapest at Costco, like $200 less then at the running room
stores

oh i just read the box it says

"Wireless Heart rate monitor - no interference"
"Use courses feature to race previous runs" ------------------ i think thats what you want

and it also has "Detailed post-workout analysis on PC/Mac"

Hope this helps

Eric