Heh, you have a big conception missunderstanding ;-)
when you install a package (may it be a .deb package, a .rpm, a .tgz, a .ebuild or whatever) this package has some meta-information which tells the unpackager (the program that actually unpacks the packaged file and installs it) which packages must be installed in order to be able to work with that package. So, when dpkg (apt-get is just a front-end of dpkg) tries to install the amule package, it find out that the libcrypto++5.1 package isn't installed. By compiling crypto++ you are installing libcrypto++ but dpkg has no idea that you have done so, since in its database, no-one has added crypto++ as "installed".
apt-get should actually automatically install libcrypto++5.1 but it isn't doing so. This is probably because you aren't useing Sid, but maybe Sarge or Woody. I'd rather suggest you try compiling aMule instead of apt-getting it. As I use Debian, I'm going to try reproducing your problem here in my box, to see what is exactly happening. Meanwhile, compile aMule... this way you'll be able to _always_ have the latest aMule release working! WOW! ;-)
Greetings!
