Using format to add leading zeroes

I have a numerical vector which contains a (poorly) formatted time 
column, which, in theory, should be HHMM, but was distributed as an 
integer, so, for 12:15 am, it is saved as "15" (e.g. HHMM = 0015 with 
the zeroes stripped).  I'm trying to use this in conjunction with 
strptime, but I'm thinking because each time is an integer ranging from 
1 to 4 digits, I probably need to coerce this vector using "format" 
first to add back the leading zeroes -- but I can't seem to figure out 
the specific parameters to send to format().  Thoughts?  I could use the 
pad0 function in PBSmodelling, but it seems to only work on one item at 
a time (not an entire vector) so I thought I'd ask here if there's an 
easy trick to getting where I need to go using on the base package and 
not needing to write a for-next loop to implement pad0.

Thanks!

--j

Jonathan A. Greenberg, PhD
Postdoctoral Scholar
Center for Spatial Technologies and Remote Sensing (CSTARS)
University of California, Davis
One Shields Avenue
The Barn, Room 250N
Davis, CA 95616
Cell: 415-794-5043
AIM: jgrn307, MSN: jgrn307 at hotmail.com, Gchat: jgrn307