The different names should not be a problem as long as the rpms provided the same thing. But in my opinion, the problem is that Mandrake is using a different numbering system. aMule requires krb5-devel >= 1.3.1, Mandrake rpm provides krb5-devel = 1.3-6.4.100mdk. Now how do you compare those two? Probably rpm is ignoring what is after the dash and considering it a release string. So what Mandrake is actually providing is probably krb5-devel = 1.3, while aMule is requiring krb5-devel >= 1.3.1.
OldFrog, if you are a curious person

you could change that line in aMule spec:
From:
BuildPreReq: wxGTK-devel >= 2.4.2, krb5-devel >= 1.3.1, grep, curl-devel >= 7.10.6, automake >= 1.7
To:
BuildPreReq: wxGTK-devel >= 2.4.2, krb5-devel >= 1.3, grep, curl-devel >= 7.10.6, automake >= 1.7
And see if it works. Do it like this:
$ tar zxvf aMule-CVS-20050317.tar.bz2
$ vi amule-cvs/aMule-CVS.spec
... edit the line...
$ tar zcvf aMule-CVS-20050317.tar.bz2 amule-cvs
$ rpmbuild -ta aMule-CVS-20050317.tar.bz2
Just scientific curiosity

I don't know who has put this requirement in aMule, but maybe it could be lowered to krb5-devel >= 1.3. Anyone knows something about this? Why aMule requires kerberos?
Cheers!