I've been told that it is possible to use AM2+ processors on a supported AM2 slot, but I'm not sure if the K8M800 is supported. I don't see much documentation for it, and a beta BIOS that could theoretically support it was last updated in 2008.
Does anyone have any advice or instructions on whether or not this is actually possible?
Normally you can check the website for details, but looking I would say no. Also, if you want an upgrade... Never buy Biostar, they are the WORST motherboard company, next to foxconn (that's my opinion, but most people will agree). Go for ASUS or Gigabyte, if you don't have the money, aim for ASROCK, MSi is alright.
Its an early AM2, plus I don't see any form of support of a Phenom II on there (that is the one your talking about right, I only know of one AM2+ Processor). There doesn't seem to be much in form a bios update that would allow you to do it either.