No, that does not appear to be a path issue. That's just plain weird.
Ok, this is a lousy way to approach things, but I would do a removal and a reinstallation of apt-get.
# rpm -e apt
then "cd" to where you have the original apt*.rpm file stored and
#rpm -Uvh apt-0.5.5cnc6-0.fdr.8.rh90.i386.rpm
Or better yet, go to http://apt.freshrpms.net
and use that one instead. That's the one that I have used successfully several times and know that it works well.
Wish I had a better answer...
I have been using apt4rpm since RH 6.2 and use it instead of up2date, yum, current, redcarpet or any of those other updaters.
Wait, just had a last thought. You don't have redcarpet from Ximian installed, do you? Redcarpet and apt do not play well together. Once I actually ended up doing a reinstall of RH9 because of that. About the only time I've ever had to do a Linux reinstall, it almost made me feel like a Windows user