New Notebook

You can get a edu discount on the MacBook as well. In the US edu online store, it says that you get $100 off for any of the MacBook line.

 

I was in the same situation as you. All the programs you mentioned work fine on a MacBook, especially sketchup works better than I thought it would. Depending on what you do with sketchup though, it can really tax your system very quickly. Even on my MacBook Pro, it has difficulty with some of the models I created (The 3D Tree components are the worst, avoid using them as much as possible).

My favorite thing about getting the Pro is the screen size. If you are at the studio all day working on projects on just your laptop screen, you will be thankful for a bigger screen. I had a 12" iBook before, and photoshop on that was irritating. Other people with smaller screens wished they had bigger ones as well.

Or you can do what my friend did. He bought a carrying case for is 20" iMac and brought it to school with him every day. It was kind of funny, but his screen space was envied...

 

SketchUp won't make you happy on the MB (I had a very annoying issue where it would leave a copy of whatever thing the tool made wherever it would go after a little while), as it might as well not have a graphics card. Get the MBP, it has a nice GPU and will handle all your tasks for it very well, as what you will be doing seems to be professional, the Pro bonuses on the MBP will suit you well.

 

Was this in OS X or Windows? I was running it in Windows on my friends MacBook and it worked fine. I was assuming the OP will be using it in Windows as well since they will be using Autocad in Windows. In this case, Sketchup on a MacBook surpassed my expectations.

Plus, sketchup isn't a Universal Binary yet is it? I'm sure it would have issues from that.

 

MacBook Pro...I'm not sure if it will last you 4 years(AutoCAD is fairly taxing, I believe), but the MacBook won't last your 4 years(if it does, you'll be massivly pushing it)

Get the MacBook Pro, in 4 years, sell it, or give it to a family member who only does basic tasks

 

MacBook Pros have only been around for 1.5 years now. If you take care of it, it should last quite awhile. I knew someone that was still using a 4.5+ year old PowerBook (it was starting to fall apart though). The biggest question is how much will architecture programs advance in the next 3-4 years. If it advances quickly, than neither laptop will last anyway.