If you are going to replace the headset, I would take the bike to a shop so you get the right bits.
Sometimes, you end up having to buy 2 headsets, to get races which will fit the frame (different diameters top and bottom on by Claud Butler).
Tools for the job for me were a big long screw-driver, a hammer, a lump of 1" x 2" wood, and allen keys (or spanners/grips, depending on the type). You also need grease - advice I was given was to pack the grease in so it squeezes out when you re-assemble, that way you know it isn't "dry".
Ideally, you need to detach all the cables from the handlebars, front wheel off, mudguard off, then that gives you a chance to work.
I'd allow at least a couple of hours if (heaven forbid) I have to do a third anytime soon!
Nige