I had a closer look at this i815 platform
it contains :
FW82815 FW82801BA SST49LF004A, which seems to be 512KiB flash
Unfortunatelly, it seems that the above flash is soldered to the MBO :-(
Does it mean there's no way I can use the system for L/B or is there some inexpensive way to correct this deficiency?
Not sure if that's a good price, but you can get complete 1 GHZ i815 systems (ie ready for use desktop) here for about $65.