The mounting points for the motherboard are different from any real standard, although the case is physically large enough for a Mini-ITX motherboard.
Any motherboard from Shuttle's *G2 series should fit the case. For Socket AM2, you could probably use the motherboard from the SA76G2 or SN68SG2.
Shuttle doesn't generally like to sell their proprietary-form-factor motherboards without a case, although they sometimes have refurbs on their official eBay store
(and other eBay sellers have used boards).