Time functions

Hi, I've got another question about time - timestamps. I need to
summarize the amount of time a user has used the system for from a table
listing the userID, startTimestamp, endTimestamp.
 id    userID     startTimestamp          endTimestamp
1     2119     5/10/00 7:32:33 PM     5/10/00 7:33:59 PM
2     2119     5/10/00 7:36:30 PM     5/10/00 7:39:27 PM
3     2119     5/10/00 7:40:01 PM     5/10/00 9:40:05 PM
4     2120     5/10/00 8:11:12 PM     5/10/00 8:11:21 PM
5     2121     5/10/00 8:12:26 PM     5/10/00 8:12:46 PM

I don't want to use the interval functions as I don't want the results
summarized by total months, weeks, days, years, hours, minutes,
seconds...., I just want the total hours eg 47.98 HOURS
I couldn't find any suitable way of doing it in the manual or in
techdocs(.postgresq.org).

Anyone have any suggestions?
Thanks


--
Ron St.Pierre
Syscor R&D
tel: 250-361-1681
email: rstpierre@syscor.com