Recently Dell made their own OMSA packages available for Ubuntu. Unfortunately they didn’t provide a version for Debian and the dependencies can not be fulfilled with Debian package only. To be able to install OMSA from Dell you need to follow the steps on their page but before you proceed with aptitude install srvadmin-all you need to download two packages from Ubuntu and install them.
Afterwards you’ll be able to install and use OMSA in Debian squeeze. No lenny, sorry. The binary versions don’t add up.