Logic dictates everything. Watch:
1. The existing processor is socket 939, for a fact.
2. The new processor is socket 939, for a fact.
3. The board uses socket 939 processors, for a fact.
THEREFORE, we can conclude that the socket 939 processor will work in the socket 939 board. Done.
Of course, this doesn't take into consideration power requirements, etc., but that can be fixed, too.