Don't need much RAM - there are two slots for DDR2, could put everything into RAM but likely won't for now. So, will just put some 512MB sticks in there, test them one-by-one. Found one:

Good! Tested it for 8 more hours, works nice. Found one more:

okay then. Next one?

Shit. Well, let's grab one that has a "tested working" sticker on it. Tested separately, good! Now let's test them together for a couple of hours:

32 hours should do it.