Hey, that's a nice looking truck.. we never got that model in Australia (well, not that I recall anyway)... shame.
Is ARB stuff easy to get in the US? - or is it everywhere like it is here (which of course it is everywhere here as it's all from here, but it's just bloody expensive!)
I can't really offer a lot of help with replacing the door handles on it as I've never even seen an Xterra, though I'm guessing it's probably the exact same handle as on the Pathfinder (though I've never had to take one of mine out).. but as far as advice goes I'd simply say that you need to note EVERYTHING you unplug, unscrew, or remove, place it all in an orderly place like a tray in the order you take it out.. and if unsure take photos on your phone as you go so that you can reverse the process and put it all in easily.
I'm sure it'll go on well.
Hey, if you are in to your 4wding take a look at my forum, trying to get more people from around the world to join up and post pics and stories to get things happening.. it's not model specific or a 'help' type forum, it's just for 4x4 enthusiasts (so hopefully it won't upset the moderators on this forum by my mentioning it - because I certainly am not interested in stealing users, just encouraging a few enthusiasts to join me as well)

4x4forums.org is where you should go, or through the link in my sig/profile etc.
If you really like your 4wding I've got some stuff (though most of it could've been done in an Cadillac!) info on a recent trip I did to Lake Eyre, the great inland salt lakes in Central Australia, lots of pics and stuff as the lake is almost full now, which is one of those rare occasions.. and you can see my Pathy in all it's glory.
Anyways, good luck with the door handle problem, I'm sure it'll be easier than it might look from the start, just take it slow, and when something doesn't go right stop, take a few minutes break and start again. (can you tell I used to be a mechanic? hahaha)