St. Paul campus is actually in Falcon Heights (a small suburb north of the western edge of St. Paul). It's not walking distance, but there is an inter-campus bus (between the east bank, west bank, and St. Paul) that runs very frequently (every 5 minutes 7am to 6:30pm, every 15 6:30pm to 10:00pm, and every 30 from 10:00pm to midnight). You could easily live near St. Paul campus and commute to Minneapolis every day. The bus has its own private road most of the way, and can make the trip in ~10 minutes depending on traffic on the Minneapolis end.
The St. Paul area I was referring to was in the Highland Park neighborhood, which has a little more life than the area surrounding St. Paul campus. It's more or less due south of St. Paul campus. There is good express bus service there, so you can get to/from the East Bank in about 30 minutes during rush hours. It's also on several bus lines that take you to downtown or the light rail station so you have easy access to campus, downtown, St. Paul campus, the Mall of America, and the MSP Airport.
Some google maps:
Minneapolis Campus (East Bank): http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=Coffman+Memorial+Union,+Minneapolis,+MN&sll=44.975296,-93.24971&sspn=0.028659,0.06609&ie=UTF8&ll=44.970992,-93.213758&spn=0.028661,0.06609&z=15&iwloc=A
St. Paul Campus: http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=Cleveland+Ave+and+Buford+Ave,+St.+Paul+MN&sll=44.917843,-93.186024&sspn=0.007172,0.016522&ie=UTF8&z=17&iwloc=A
Highland Park: http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=Cleveland+Ave+and+Ford+Parkway,+St.+Paul+MN&sll=42.395618,-72.531524&sspn=0.014959,0.033045&ie=UTF8&ll=44.917843,-93.186024&spn=0.007172,0.016522&z=17&iwloc=A
Another nice place to live in Minneapolis: http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=Hennepin+Ave+and+University+Ave,+Minneapolis,+MN&sll=44.984671,-93.187182&sspn=0.007164,0.016522&ie=UTF8&ll=44.986337,-93.25308&spn=0.006981,0.016522&z=17&iwloc=A
For the last link, look in the neighborhoods south and east of here - there's much less bus service to the north and west.
I should mention that I'm renting a place from Dinnaken Property Management (http://www.dinnaken.com). They have a couple of undergrad apartments, and then two senior/grad apartments. All four of these places are just East of campus, and their rates are pretty reasonable for the location. They've been really pleasant and helpful all year. The two grad places (Tairrie House and Fulton Townhomes) tend to fill up quickly, so you may want to get on the waiting list now if you're interested. Again I'm not affiliated, except that I'm renting here.