I'm experiencing the same problem. I never made a mod for forge before (did for make some for bukkit though), so plaese tell me if I do something wrong.
So here is what I did:
1: Downloaded forge (version 6.5.0.471, current recommended build)
2: Unzipped the file.
3: opened a new terminal in the /forge directory.
4: chmod +x ./install.sh
5: runned ./install.sh (result: pastebin)
6: cd ./mcp
7: runned ./recompile.sh (result: pastebin)
I'm running linux (Ubuntu 12.10) with OpenJDK (1.7.0_09)