Hi Jim,
Not sure how the pricing goes there, but for probably not much more than a converter you could maybe consider a PII/Celeron style motherboard?
There are many advantages to doing this - one big one being that the $$$ goes to something much more expandable than what it sounds like you have now. Also things won't be choked down through a converter, the glue chips are a lot better in the PII boards vs. PI, etc.
There are a few companies that make AT style PII boards which you would need to keep from having to also replace the box, power supply, etc. I know ASUS makes one and think that ABIT does too.
Unfort, don't know anything about the converters you would need to use your present board though.