Zip,
To attach them at the bottom bracket, put a P-clamp around the chainstay bridge (assuming you have one) with the flat (flush) side facing backwards. Then run a button-head allen bolt through the fender (it should have a couple mounting holes near the bottom end) and through the P-clamp and tighten onto a nylok nut. You may need to trim the fender or drill a hole so you get the right positioning -- the first-time mounting of fenders on a bike can take 2-4 hours to do it right, but after that, even if you replace them, it takes 15-30 minutes.
On the oversize fenders, don't knock them. You may figure it's less hassle now, but the narrower fenders tend to shift position slightly every time you lean your bike against a wall or wherever, and you're frequently stopping to adjust them so they don't chafe a tire. You help with clearance by mounting them a bit farther from the tire than you might initially think (this is especially true of Raceblades, whose struts have a bulky plastic fitting on the underside of the fender which really cuts down on effective clearances). But if you get the oversize ones, all you need is a pair of inexpensive tin snips to trim them neatly to fit. You most likely need to trim them anyway (at the chainstay bridge, almost any fender needs to have the sides cut away so they go down past the chainstays for the best protection of your bottom bracket and crankset). I recommended RaceBlades to my fellow team members when they first came out, and we were always stopping to adjust them. When the RaceBlade XL's came out, I tried a pair and this winter, everyone is either on oversize fenders or the RaceBlade XL's. Just a friendly hint -- you can't stint on your fender mounting or it comes back to bite you when you're riding.