I feel your pain! Most software written by and for astronomers is pretty horrible code, poorly commented and documented. I've used a number of other astronomy codes, but unfortunately not that particular one so I can't give you specific advice.
More generally though google searches can be surprisingly helpful for this sometimes. The most specific phrase may well pick something up. It really depends on what your problems are, they may be more to do with general problems that might have solutions in general developers forums rather than anything specific to that code or astronomy. If you give some more details about what problems you are having that might be useful. Remember there is also a coding sub-forum here that could be useful.
If it is more to do with the actually calculations in the code (as opposed to problems compiling, linking etc) then it's harder as there is not likely to be a lot on the web for the specific issues. It might mean that you need to really read through the code get an understand of it right from the bare bones. I've had to effectively retro write my own documentation for codes in the past that didn't come with any, based solely on reading the code itself. This is not as fun as it sounds, but can be a useful process as you really have a chance to understand how it all works and maybe pick up some neat coding tricks as well.
Of course it depends how good your coding knowledge is. If you don't really know C and there's no documentation you're probably in some trouble. In this case either learn better C (good to do anyway) or you might have to ask the authors some questions. In this case though it pays to be as specific as possible, it's not likely they will answer an email saying 'how do you use your code?', you'd really need to say what you've tried and the specific issues you're having.
Are you doing this for a University project? If so you must have a supervisor (or advisor depending on what continent you are on) that should be able to help. Don't be afraid to ask silly questions, it's better than wasting time on a problem you can't solve!
Edit: One more thing I forgot to mention, there is a forum http://cosmocoffee.info/" that has a section for discussing problems with astronomy codes. It is mainly a cosmology site and the codes discussed are generally cosmology, rather than astronomy, related but it might be a good place to ask for help none the less as it is frequented by professional astronomers only, so there is a good chance that someone has used this code. Again though, you will have to be more specific about the problems you are having to get meaningful help.
