Should I negotiate compensation from my offer letter?

I just received an offer letter that's offering me $30K/yr but I think it's rather low considering that most of the duties called for I have experience with and the fact that although I'm a recent grad from a prestigious university, I expected more. I mean in college I was working and making $4 less an hour than this job is offering and now that I graduated I go up a tidbit?! But, on the other hand, I don't want to seem greedy because I know many well educated, experienced people are unemployed right now. So with that said, I want to know your opinion if I should negotiate on that compensation. The interviewer says she's open for negotiation but after 3 months. How should I go about doing this? What should I say? When should I bring this up? What would you do?