My wife is in a similar spot - she got her ungrad in elementary education with a history minor (in 1997!) and is now interested in going back for historical archaeology. 3.7+ GPA and ~1400 GRE, but after talking to some professors she decided her resume was too thin to apply this year. She instead contacted some local archaeologists (UMD, MD Archaeological Society, Smithsonian Institution) and volunteered her time for the year. She spends 20-30 hours per week on a couple of projects under some great people, gaining knowledge and experience while they get an free set of hands and a fresh mind in a year when funding is pretty thin. She will mostly finish up this year, and start over in IL (my grad school) working with local professors. That way, when she applies for AY2010-2011 she will have a very solid 18 months of research experience, opportunities to be published, and great references including one or more from her school of choice. All for free!
I would heartily recommend something similar for you - few professors will turn down the free help, and it is a great way in.
If anyone has any other suggestions (other than classes - we know that one) to improve one's odds at jumping fields, I would also appreciate it!