I am running Woody. I also just downloaded (through the Debian package 
page) ppp_2.4.1-4_i386.deb, and tried dpkg -i. Same problem. So, I changed 
the command in /etc/modutils/0keep to something harmless (ls) and tried 
again. This was the result:
---
(Reading database ... 65884 files and directories currently installed.)
Preparing to replace ppp 2.4.1-1 (using ppp_2.4.1-4_i386.deb) ...
Unpacking replacement ppp ...
/etc/modutils/actions: post-install: command not found
/etc/modutils/actions: post-remove: command not found
dpkg: warning - old post-removal script returned error exit status 127
dpkg - trying script from the new package instead ...
/etc/modutils/actions: post-install: command not found
/etc/modutils/actions: post-remove: command not found
dpkg: error processing ppp_2.4.1-4_i386.deb (--install):
 subprocess new post-removal script returned error exit status 127
/etc/modutils/actions: post-install: command not found
/etc/modutils/actions: post-remove: command not found
dpkg: error while cleaning up:
 subprocess post-removal script returned error exit status 127
Errors were encountered while processing:
 ppp_2.4.1-4_i386.deb
---
   This was, mind you, using dpkg -i. So what do I do? Every time I run 
apt-get, it sees that it has an uninstalled upgrade for ppp and tried to 
install it. The bug list  didn't seem to have anything about it. I don't 
know the internals of the packaging system, so I don't know how to remove 
it from the queue.
   :Peter