Hi, Steve.
As Alvin Brown said, read your motherboard's user's manual. Then visit the
mobo maker's website. Often, faster CPUs come to market after a mobo has
been built, shipped and sold. No way the original owner's manual could have
known about these, so look on the website for up-to-date info. Also, be
sure to check there for an updated BIOS. Often a later BIOS will enable us
to use a later CPU or RAM or other upgrade.
Is VIA KT266A the model of your mobo? Or of the chipset on a mobo made by
someone else, such as DFI? If you post the exact make and model, someone
here might recognize it and have some specific advice.
RC