There were several variants of M925; M925, M925G, M925L, M925U, M925LU, and a few others.
I assume since you report four memory slots that it is one of those combo motherboards that features 2 x 168-pin SDR slots and 2 x 184-pin DDR slots. You cannot use 168-pin and 184-pin slots at the same time.
The board will support:
168-pin PC100 or PC133 unbuffered non-ECC SDRAM 3.3V up to 1GB total (512MB x 2)
184-pin PC2100 or PC2700 unbuffered non-ECC DDR SDRAM 2.5V up to 1GB total (512MB x 2)
Technically, the chipset can support up to 2GB (1GB x 2) but due to the age of this board and BIOS, I would recommend no more than 1GB (512MB x 2).
For best compatibility, do not use any memory marketed or advertised as "high density".