Karen, you asked a very timely question. This is a very tough market. Our students graduating from the Heinz School at Carnegie Mellon are getting offers that are lower than what students graduating a few years ago received. So you might need to make some concessions to get your foot in the door.
The first step is to determine your reservation value: what is the lowest offer you will accept from a particular organization. This is based upon what you think the market is like for a person with your skills and how urgently you need a job. You should feel ok to decline offers that are lower than this amount.
The second step is to keep searching. Also, you should identify the other aspects of the offer that are important to you that may be easier for the other side to give you. Is title important? Tuition benefits? Flexibile work schedule? The ability to get extra training? Organizations may be more willing to give you these things when the economy is bad.
Third, be willing to adjust your expectations based upon your experiences. If you get a series of offers (say 5 or so) that are all unwilling to come up to your salary level and you feel that otherwise the jobs are a good fit for you, you may have to revise downwards your salary expectations.
I hope this helps! Organizations know that when times are tough they have greater bargaining power and may be less willing to negotiate salary. But, that doesn't mean that other aspects are not up for negotiation! Best of luck!