The pictures you've posted show a broken gaiter. You can replace it, and grease the slip portion of the propshaft without issues.

Some people have also brought up the universal joints. This is unrelated to the question you've asked, so this might be what is confusing. They ARE important to replace on Discovery 2. It does require a press or vice or something to replace them. If by "centerize" you mean balance, you shouldn't need to balance the shaft just for a joint replacement, most of the time.

You would need to take the factory shaft off and put grease fitting on it.
Problem is you need to take it apart
due to the drill shavings getting into the existing oil.

I'm looking and the boot that I'm referring to or "Gaiter Propshaft" looks to me like its for extending and retracting of the drive shaft, it is separate from the function of the U joint is it not? So are you guys warning me that I not only need to fix the boot, but check these U joints?

nevermind this was answered before I finished posting LOL

Ok so there is no need to balance it. And yes that is what I meant jafir. :)
As for putting the grease fittings, yes i would think you would have to take it apart. I'm sure them shavings would have a party in there every time it spins if you didn't. I do have a press and several vices and the U joint only costs $20 at Atlantic British. Sounds like it would be a good idea to put a new U joint when doing the boot. Especially since I may be doing some long travels in a couple of months.

8 years and 99k on the clock. Its time to replace the u joints. They live next to a cat and get baked out every time you start your truck. Just lubing them at this point isnt gonna do much.

ok so I'm replacing u joints and the gaiter. Thanks Everyone!!!

I'm rebuilding the front shaft and I need to install the boot. I need to separate the 2 parts of the shaft to put the boot. Does it just pull apart? Or is there a trick to it?

It does just pull apart. Be sure to mark it first, though. There is a key spline that will keep it from fitting back together properly if it isn't lined up just right.

Don't forget to replace the centering ball also or you will have a failure shortly after reinstalling.