I am having the exact same problem that kineticdave had the other day trying to install althea. he fixed it by commenting out the ssl refs in the Makefile...I don't really want to do that. I've got OpenSSL install properly, and did add the '-I/openssl-0.9.6a/openssl/include' line to the Makefile as suggested. here's the complete error:
g++ -Wall -ftemplate-depth-30 -g -I/openssl-0.9.6a/openssl/include -c Althea.cpp `gtk-config --cflags`
In file included from Message.h:10,
connection.h:13: openssl/ssl.h: No such file or directory
connection.h:14: openssl/rand.h: No such file or directory
make: *** [Althea.o] Error 1
from you post, it looks like you include -I/openssl-0.9.6a/openssl/include which would make the compiler go from your root, i.e., / and look for an openssl-0.9.6a folder and then go up from that. I think that is what it will do. Try to find the absolute path to the included header files. If you find that the path to the header files is not something like this: /blah/blah/blah/openssl/ That is, the openssl is NOT the last directory before you get to the header files, then you are going to need to edit the connection.h file and I can help you do that.
I think it is becoming clear that althea needs to get autoconf to help people through different configurations. With the addition of SSL, we've gotten a wide variety of installation problems. We need something to alleviate that.
Let me know how it goes.