Port confused after 10.4 to 10.5 upgrade

[Roland Besserer]

After upgrading from OSX 10.4 server to OSX 10.5 server and running a  
"port selfupdate" I can no longer install new packages.

I had MacPorts 1.5 installed on 10.4 and upgraded to 10.5 (both  
server) a while back, but didn't touch MacPorts. Attempting to install  
a couple of additional packages yesterday, I got library version  
mismatch errors and decided to run a selfupdate. That successfully  
upgraded the port installation to 1.7

Whenever I try to install a package now, I get the following error:

error: $MACOSX_DEPLOYMENT_TARGET mismatch: now "10.5" but "10.4"  
during configure

Any way to fix this?