Modest Mouse has a song called "Sleepwalking" and the opening riff and
background music  sounds like
an old 50's song. I would like to know what the name of that song is.

Hi laconik:

Thanks for the interesting question. 

Actually, the 50's instrumental that you are searching for is called
"Sleep Walk", made famous by brothers duo Santo & Johnny. You can
actually listen to some of it at:

SleepWalk Home Page
http://www.santoandjohnny.com/

More about Santo and Johnny Farina can be found at:

Santo and Johnny
http://www.history-of-rock.com/santo_and_johnny.htm

As you already know, the group Modest Mouse did a cover of "Sleep
Walk" on their CD "Interstate 8", where they added lyrics of their own
to this famous instrumental.

MODEST MOUSE: Interstate 8
http://www.cmj.com/articles/display_article.php?id=25534

Search Strategy (on Google):
* "Modest Mouse" sleepwalking instrumental
* "Modest Mouse" sleepwalking instrumental 50s
* Santo & Johnny Sleepwalking
* "Santo & Johnny"

I hope this helps put your mind at rest. 

websearcher

It was direct and a quick response. It helped answer my question. Great Job

Hi laconik:

I'm glad I could help you answer your question. Thank you for the
generous comment and tip!

websearcher