If its so complex what is the point of usage? Only for those who created core. There is nothing to compare, no info no tutorials, manuals anything,
Remember that TG68 is a spare-time project for someone who was generous enough to share his work, in the hope that others would find it useful. It's not a "supported" product - those generally cost money!
I'm only just starting out in FPGA programming myself, so I can't be a lot of help - but if I were getting absolutely no response from the core, I'd be looking at the reset signal and the clock signal.
At least person other than Tobiflex has successfully used the TG68 in a project, though - http://code.google.com/p/fpgagen/
- maybe reading the source of that project will help you?