Help with multiple outgoing servers in mail

[John]

We just got cable internet (wohoo!). Fast and wireless (PB G4 550Mhz, 
10.3.1).

However, our provider blocks all but it's own ISP from sending mail, 
"forcing" me to use their smtp server.

This isn't a big deal, as I can easily select a different server when a 
piece of mail fails to send. It is annoying, however.

Is there some script, hack, or way to have mail.app - based on my 
network setting - to change which smtp servers to use? Can I create two 
sets of preferences, and swap them when I am at school/work, and then 
when I am at home?

Because when I am at school/work, I doubt I can send my mail though my 
ISP's server.


Thanks!

PS - I am cross-posting this because it borders on both x-apps AND 
mobile computing.