We'll use a modified version of libapt in Kalypso. That's decided and I am working on it. The RPM part is working fine since the Apt version we're baseing ours on was Conectiva's Apt 0.3.19cnc55. The problem is that Debian changed its libapt at some time in the past.
Also, when porting to RPM, some of the deb code stopped working so I have to fix that. I installed a Debian system on a VMware box and now I'm working on getting our libapt working on Debian as well as RPM-based distros.
As a side note, Conectiva Apt was not ready to be compiled with gcc3 which gave me a good headache.