Well, the deal is... you can't buy any gun from a private party across state lines unless you intend to live in that state. From the way I've interpereted it, the ATF has ruled that it's ok for someone who has two homes to buy in either state, so I would think of where I go to school as my second home.
Unfortunately, Michigan law sucks ass and there's a catch: you'll need a Michigan drivers license to get the "pistol" purchase permit bullshit. You have to go to the police station of the city/town of your (MI) drivers license home address to get the purchase permit bullshit. Then, you have to take it to the person you're buying the "pistol" from, and bring the "pistol" back to the police station (within 10 days) for a "safety inspection".
Now, as for the guy telling you he needs your SS#, he's an asshole. That's a load of crap. You just give him the permit and he fills out half of it, and the gun is sold.
*Note: I say "pistol" because in Michigan, a rifle is called a "pistol" if it's under 30" in length (more bullshit laws).