I was in a very similar situation to you not 7 years ago. i was given a series III 88 for christmas in 8th grade and it had been garaged since 1979. At least I had a solid frame and good wiring to start with.

to free the engine, pull the spark plugs and put marvel mystery oil down there and let is sit for a few days, then refill and wait some more, and you never know it might just free up.

When and if it is free, put new spark plugs in it, put a new battery in it, check the carb for debris, and then put a little fresh gas down it and see if it kicks. I was surprised when my 88 roared to life after 26 years of neglect and minor maintenance.

hopefully nothing is wrong with the engine or transmission, typically when one of those failed they either junked the truck or parked it. If those have/had oil in them the whole time hopefully the insides are still good.

Expect to replace everything rubber and all of your hydraulic systems will need a good sorting. Obtain a green bible or the workshop manual cd and it will provide step by step instructions for everything you will ever need to do to your rover, makes it less like a challenge and more into a big set of Lego's. Post pictures up here and more often then not the forum can also be an invaluable source of information as well.

What i cannot stress enough is take your time and do everything right the first time. When people told me this I thought I knew it all and half assed a few things to get it on the road, which ended up taking 3 times longer to fix in the long run. The trucks been sitting for how many years? A few more months wont hurt it.

The hardest part of the ordeal for me was resisting the teenage temptation to beat things up and treat it like a modern disposable car, especially in the woods. My 88 started out with a straight body with minimal dents, and now there isnt a straight panel on it. I've blown and rebuilt my transmission twice, rolled it over, and sunk it up to its dashboard in water (not all in the same day). I regret it now looking back as most/all situations were very avoidable, but I have a story to go with each dent, and the aluminum can be annealed and bent back when I'm done having fun with it one day.
Let the journey begin,
-Rob

p.s. as an incentive to finish it while your still young, its the ultimate chick magnet