Depending on the model fo strat, you may have to do some body routing. Check under the pickguard. If you have space for a full sized humbucker, all you will need will be a new pickguard.
Most Fender Strats have HSS routing with an SSS pickguard, so like Benjy says, all you'll need is a new pickguard. I think some of the Fenders have HSH routing, but that wouldn't change anything. What kind of guitar is it?
