Let's look at your items 1 at a time

-For the type of riding you will do, an XT derail. will be more than fine.

-The brakes. This item will probably be the deciding factor for you. Disc brakes are great for off road riding. I would usually say for someone riding mostly on the road, discs are necessary. However, they are great for riding in snow and wet conditions. The Pine Mountain has Avid mechanical brakes which several reviews have raved about. It would cost you more than $400 to upgrade to discs if you bought the 2000 bike (provided it has the proper mounts). So, if you think you need the discs now or in the future, the 2002 is the choice. Otherwise, V-brakes provide the next best stopping power.

-Fork leaking oil? Doubtful. I wouldn't worry about it. The shop should take care of it anyway since you are buying it new.

-Threadless refers to how the stem mounts to the fork. You want threadless, but I'm pretty sure a 2000 Pine Mountain should have a threadless setup. Only low end MTB bikes have used threaded (opposite of threadless!!!) setups for the past 5 years or so.

Good luck, hope that helps.