You sort of answered your own question. First of all most of these were made for 26" or smaller wheels, they may not accept a brake, and the diameter of the steerer tube may be such that a headset for a road bike may not fit. Lastly these are designed for a much more relaxed geometry so there may be some handling issues.
A little searching on ebay may turn up an inexpensive suspension fork.... but then again you also run into issues in changing the geometry.
__________________
“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk