http://www.bikepedia.com/QuickBike/B...=F1X&Type=bike
Is this your frame? If so:
1) That's a 1 1/8" threadless steerer on it, stock. Just about any road or CX fork should work with it. Is there a headset in it right now?
2) It has vertical dropouts, so a typical ss/fg setup likely won't work. On the bright side, most, if not all, singlespeed tensioner kits (such as the Surly Singleator) come with cogs, spacers, and lockrings that slide over typical shimano freehubs- so get yourself a road wheelset, a tensioner kit, and any carbon fork.