Part 1 of several - Converting a varchar to an interval

Hello,

I have several large tables, over 100 million records each.  One of the fields 
is callee 'duration'.  It is a varchar that contains what is essentially an 
integer that is the duration of an event in milleseconds.  Could someone tell 
me a simple way to convert a value such as 134987 stored in a varchar into an 
interval?

This will dovetail with my next question. 

Thanks for all the help both now and previous.

Shawn