NetworkManager in Lenny writes it’s PID to /etc/resolv.conf:

### BEGIN INFO
#
# Modified_by:  NetworkManager
# Process:      /usr/bin/NetworkManager
# Process_id:   2869
#
### END INFO

This leads to etckeeper displaying a change every reboot:

This patch to the debian package stops NetworkManager from writing the INFO block to /etc/resolv.conf.

Alternatively, there is a backports package for lenny with an updated version of NetworkManager.