Personally, I would skip Irish moss with a pre-hopped extract kit, and, unless you are adding hops, they (pre-hopped extract kits) don't have to be boiled. I've brewed 2 of them (pre-hopped extract kits) recently to see how well I can get them to turn out. This is what I would do:
1. Bring 2 to 2.5 gallons of water to a boil, turn off heat.
2. Add pre-hopped extract, and spray malt (DME), stir gently to get it all dissolved and mixed. If you use dextose, don't use a lot. I've added 4 oz (along with 1 lb, 12 oz DME). Let it sit 10 mins or so now.
3. Cool the wort by your method of choice; I'd try to get it to about 70 degrees ballpark.
4. Add top up water to get to your final volume, typically 5 gallons.
5. Stir, check gravity, aerate and add yeast.
The key to getting good results out of these pre-hopped kits is much the same as with any of the other brewing methods: use fresh ingredients (particularly the liquid pre-hopped stuff), good sanitation practices and control of ferment temperature. Also, skip the included yeast and go get a good quality dry yeast or even go with a liquid yeast. For simplicity's sake, my suggestion is a good quality dry yeast, and re-hydrate it, though if you want to keep it as simple as possible even that's not really necessary.
So far, I've found that I can get a pre-hopped kit brewed like this in a little less than 2 hours, including set up (my brewing equipment is in my basement, and I have to bring it upstairs when I brew) and clean up, and I'm not a rush rush person, if you know what I mean. The results thus far have been pretty good, though honestly I still prefer my partial mash brews over the pre-hopped kits. It's a good way to start for sure, and I don't think you will be disappointed with the results. I'm going to continue to brew them occasionally, and try some of the various styles available.
EDIT: stratslinger mentions it, but I don't use a secondary either. Three (sometimes 4) weeks in the primary and then bottle. Check with the hydrometer, of course, to gauge fermentation progress and completeness before bottling. Bottle condition minimally 3 weeks @ 70 degrees.