I have drilled a steel fork to take a mudguard. Took bloody ages and the result (due to breakage of several drill bits in the process) wasn't all that central. This was OK for a mudguard - but would be worrying if the hole was for brakes, which really do need to be spot on central for them to work well and not rub etc, so I wouldn't advise you do it yourself. I was told (by LBS) that depending on which fork you have, drilling it could actually compromise it's strength. My fork was basically scaffold tubing (and was already bent anyway) so probably no harm was done, but a lighter weight fork may have suffered. If you have the bosses for Cantis or V-brakes why not use them? You can get Dia Compe V-brake levers which work with drop handlebars if you want to use V-brakes, but modern cantilever brakes (that you can use with ordinary aero brake levers or STis/Campag Ergos) are very good - especially the 'frog legged' ones where you get greater leverage.