If you're upgrading to a new AMD Athlon 64 CPU then you need to know whether your motherboard (or the motherboard you're purchasing) supports it. AMD's latest revision of chips and their new dual core chips require BIOS support to allow them to work. Anandtech explores this further.
To try to shed some light on the current BIOS revisions and processor compatibility we took a closer look at the state of x2 processor support among motherboards. In many ways the adoption of x2 is faster than we expected, but there are still gaping holes in x2 and Rev. E processor support. Hopefully with this guide and a little research you can find the perfect motherboard home for your new Revision E or x2 Dual-Core Athlon 64 processor.
There doesn't seem to be any further info on certain VIA-based motherboards not supporting X2 electrically, as we reported from Computex, although the article does say there are some VIA K8T890/K8T800Pro with X2 support.

Read the article at Anandtech.