In the past all references I've tried (e.g. Kingston's memory configurator) have said that the motherboard is maxed out. Last night I tried Crucial's program, and lo and behold it says that I can put two 1GB, 184-pin DIMMs. Since it correctly identified the computer (exact model etc.) I think I can assume that it probably knows what it's talking about. On the strength of this, and since Crucial guarantee it to work, I've ordered one and will get another if it's OK.
I'm pretty sure I've tried Crucial's program before, and got the maxed out result, so what baffles me is why I was previously told nothing more could be added. Has there been some change in DIMM compatibility?