Label with substring of metadata

[David Isaacson]

Hi,
I want to label my map with a substring of the metadata.  I've got a 
freeway map, and all of the freeways are labeled as "Interstate 5" and 
"US Highway 6".  I just want the number.

Is this possible?

I thought I might try to add that data to the .dbf file, using Excel.  
And it works using shp2img, but when I use ka-map to create an 
interactive map no roads are drawn at all (and no error messages are 
given either).  So what the hell is going on?

What's the right way to add metadata to a shapefile (assume I can't 
afford to buy ArcGIS)?  And is there an easier way to do this whole 
labeling thing?  Thanks.

David