Timing belts aren't that difficult. Just make absolutely sure that you line up the timing maks perfectly. If you aren't sure if it's right it probably isn't, do it again.
You'll probably need a puller of some sort to remove the alternator pulley off the crankshaft, they tend to be a very tight fit as it's the friction between the faces as opposed to the keyway that actually drives the pulley. The keyway is there to stop the surfaces welding together if it were to slip.
Apart from that the best advice i can give you is just take your time and be totally methodical about what you do.
Chris