I believe it was a mATX mobo

It was mATX, and the case was the one you saw at LAN. It was one of the many eBuyer models that were all the same (with different side panels), but they don't seem to do them anymore. You are very unlikely to get a small case that fits an ATX mobo, trust me, I tried.

Yeah, tis a shame.

Can't really find any good mATX ones.

Skillers mobo was a good find.

Yeah, I managed to get an mATX mobo that was using a chipset (P45, IIRC) that was typically only used on high end ATX equipment. I don't think the LAN-Party motherboards exist anymore, but last I checked Asus were doing an mATX 775 mobo, they may be doing one for the i series.