There's two famous schools for guitar:
Berklee, based in Boston, that lots of famous guys have attended (Quincy Jones, John PETRUCCI, Steve VAI, Al di Meola, John SCOFIELD etc...) where lots of cool folks hang around. The only problem is that it's VERRRRRY expensive...
The GIT (guitar institute of technology) is a part of the Musician's institute, in LA. Paul GILBERT has attended the GIT, and that's the only one I can remember.
Those schools are state of the art schools, you learn with pros, working musicians, you get to play with your idols when they come through master classes, you can record things in their studios, and they are really opened towards the music industry world...
As for the system Gulder, that's pretty much the same as every University in the world:
For every semester class you take, you get a credit (if you pass of course) and you can take up to 30 credits a year (I don't know if that's the correct number, but it's for the example) that means you have 15 classes per week, some are master classes, some are open counseling, or one on one instructions with a pro.
So you need to attend the school several years to actually have the diploma, nothing new there. If you pass every class you have taken, to get 120 credits, you must have attended the school 4 semesters (4 times 30).
As for getting in, of course you send a tape, but the chances aren't slim. Why would they kick some guy that's ready to pay 3000 dollars for 6 months of instruction? As for scolarships, now there's a slim chance. Even Steve VAI payed to attend Berklee.
Those schools also offer non-diplomas classes, like summer workshops, so you might want to check this out to.