According to this howto until kernel 2.6.15 you needed a patch to run it correctly
http://pptpclient.sourceforge.net/howto-debian-build.phtml
I am running Debian Etch Kernel 2.6.15-1-486 on an x22 thinkpad
'MPPE (Microsoft Point-to-Point Encryption) support requires an additionnal kernel module, provided by package kernel-patch-mppe or in linux kernel version 2.6.15 and above.'
The support should be built in, no?
Any help appreciated
Anthony