Nope! That didn't work. (Also I use IMAP, not POP, but the same should apply with POP).
To give you a little bit of background, I have a linux imap server running on the internal network at home, and a port forward through a linux proxy server that forwards my IMAP from outside the network. For some unrelated reason, I haven't been able to access the server from the one outside address, so I need something like this.
Here's my script (after hunting through the sample applescripts that work with Mail.app) NOTE: *should* work with POP too. But I don't have POP so I can't test it. YMMV, use at your own risk :-)

on run
set myResult to display dialog "Where are you?" buttons {"Home", "Outside"}
tell application "Mail"
if the button returned of myResult is "Outside" then
set server name of account "Default" to "outside.domain"
else
set server name of account "Default" to "internal.server"
end if
end tell
end run

(bah, tried to add in whitespace there but it didn't really work. it's basically the same formatting as the one on the original comment, just change the "set server" lines (and I cut out a bit of the other unnecessary stuff)).

My previous comments pertained to using the script for Entourage. Apparently, Mail uses a different set of naming conventions. Open Script Editor, the open the dictionary for Mail to be sure.