"microATX was explicitly designed to be backward-compatible with ATX. The mounting points of microATX motherboards are a subset of those used on full-size ATX boards, and the I/O panel is identical. Thus, microATX motherboards can be used in full-size ATX cases. Furthermore, most microATX motherboards generally use the same power connectors as ATX motherboards,[6] thus permitting the use of full-size ATX power supplies with microATX boards."
from:
http://en.wikipedia.org/wiki/MicroATX
The wattage should indicate max draw, but I haven't thought about this stuff in years.
You may want to call the manufacturer of the board (microATX is a standard, not a brand). They should have a customer support number.