Like Mike said...write this one off to experience. And get some external mics.
Well, to my ears, cutting bass in audacity and adding some treble helps a lot. I don't won't to write it off and believe that that is what post processing is for?
To an extent it is, I agree.
There are limitations at which post production does well, especially without introducing other problems (due to digital artifacts related to EQ processes or other items), thats really what the first two replies were alluding to.
Some rules of thumb I have for 2ch editing are as follows:
1) broad swaths of soft EQ are almost always ok. (so say; a +2db in a gentile bell shape between 500hz and 10khz).
2) narrow "surgical" edits in EQ can be ok
or very problematic (so say a +3db between 500hz and 550hz).
3) It's rather uncommon that you'll be able to bring out more of one instrument without adversely affecting a second one, as most instruments share similar frequency bands.
On #3 specifically: you end up trading one instrument poorly represented for an improvement there, but a detrimental effect on other instruments. It's a trade off, there are no easy fixes there. For #2, the reason this could be good or bad is entirely dependent upon your playback. I keep a number of headphones handy (hideously expensive, cheapies, and stuff in between). When I do corrective EQ, I'll listen on my standard set, and then test drive the edits with my other listening setups and finally in my car and on other speakers. If it sounds good everywhere, then I've made improvements, if not, I need to really think about what went wrong. That listening is a skill set that takes practice.