I'm assuming that's the one on Washington near the U. You can simple hop on a campus connector bus (a big maroon and white bus that says "CAMPUS CONNECTOR" on it and is free to public and college students). It shuttles people back and forth from the Saint Paul and Minneapolis Campuses.
As you exit the Radisson from the front (an Applebee's will be on your left and a starbucks on your right), take a right and cross the street to the corner with a coffee shop called "Expresso Expose". Cross Harvard Street and you'll see a bus stop shelter. It will probably be full of kids, it's a popular stop (It is in front of a building called Moos Towers). Just wait for any campus connector (some say limited stops, I'm not sure where they stop anymore, I haven't had to use that bus service in two years thanks to my Peugeot. ). You can enter the bus from the front or back, since it's free. Make sure you're going east, not west! The bus will have 5 or six stops before you'll want to get off. You'll cross over onto the Saint Paul campus, and depending on where you need to be (I'm assuming the Pomeroy Student Center), you can get off on the Gortner/Buford stop.
Here's a map so you'll know where to walk to.
http://www1.umn.edu/pts/maps/spcc.htm