With respect to brewchez - no, don't put priming sugar in your keg - it works against you and can throw the taste of your beer. Moreover if you have a good, sealed keg you won't lose C02 and in fact the pressure will help keep the beer carbonated to just the right atm.
What I do is condition my beer down to 45 degrees (an ale) and when I'm ready to keg it, I use a carbonation stone on the inlet:
I got mine from MoreBeer.com and it works great.
The key here is that the beer is cold - that helps absorb the CO2. Pushing the CO2 in through the stone helps diffuse the CO2 which helps it go into solution quicker. You don't need to shake the keg (which is what most places tell you to do) - just let the CO2 pressurize to about 25-30 psi.
I let mine sit for a few hours and then bleed down to 12 psi or so - and it's ready to drink within a few hours. It won't be perfect, but it will be carbonated.
My kegs usually take 24 hours or so to come to the right amount - but be careful, make sure you set the valve to the right psi - if you leave it on and leave it up at 35 psi your beer will over-carbonate and you'll be sad.