Hey Mike,
I‘m in Sydney… oi oi oi!
Just saw the advertisement on nth-west -
“Snap Server 2000/4000 - Motherboard (DIMM type)” - So the answer is yes they are interchangeable!
The positives are that there are a lot more of the 2000’s out there than there was of the 4000…
Buying it from N/W at least you would be 99% sure that for your money (the US$ clams + freight) it will work and if it doesn’t it’s a long way to return it...
You also could see if you can pickup a snap2000 for a bit less expensive around, but the negatives are; The unit may turn out to be a v1 or its board could be completely dead, this could be managed by grilling the seller prior to the auction close… So you would be back to trusting someone on eBay
(I hope you gave that guy a bad rap on his eBay feedback page, the naughty naughty Man

).
If you can wait you might get a surprise, I will definitely keep an eye out for you to see if I can find you one, but your best bet is to do an Australian search on google of any PC recycler you can get to show up on a search then email them with a note and you might just get lucky?
If you were to locate a recycler with a snap in Sydney I would be happy to check it out for you if you send me the details… I can even organize a cheap freight to you through work…
Don’t feel bad about having a 4000 that has a dodgy MB…
Right now I have a;
Snap 2000 that needs a CPU fan (a recent occurrence)
Snap 4000 that works with 3 drives or less as the PSU is on its way out
Snap 1100 with what appears to be dead board.
Snap 2200 with what appears to be dead board.
Snap 4100 with 1x 40GB drive but also missing 1 Drive Bracket.
Matt
(The emoticons are for; Mr "you know who you are!")