I want to install a floating, click floor in a new walk-in closet. The length is 15'; however the width varies from 76 1/2" to 77 1/2" across the length! I want it to "look straight" when I enter through the door. [door is on 15' wall] Can I START at the entrance and work towards the back wall? Do I need to rip last row of boards on angle? My moulding is approx. 1/2" thick. Thank!!!!!

If you are laying the floor in the 15 foot direction, aestetically, you will want the floor to be parallel along the door open, and therefore will also be parallel along that 15 ft wall.
This means the opposite (finishing) wall will be off parallel by one inch. Not a big deal, especially in a closet space that will presumably have things in it that will hide the sightline along that interior wall.
BUT, before you start, measure the width of an individual panel and divide that figure into the 6 1/2 (approx) foot dimension to make sure the last panel will be sufficiently wide to allow for that tapered "rip" along your finishing wall. If it isnt, you will need to rip some off your starting point to allow for a proper width final piece.
Hope that helps.

Thanks a lot. That sounds good. My door is on the 15' wall. If I start along that wall, as you suggest, the "groove" will face the wall & doorway, correct? Will that side of the board work with a transition or reducer moulding I'll need to meet the thick carpet in the doorway?
Thanks again! HG

Yes, the groove will face the door opening. The proper moulding for this junction to carpet for a float floor is a t-mould. If it is a heavy broadloom, you will need to cut the underpad back about an inch from the end of the carpet to allow it to compress enough. An off-set t-mould could also be fabricated to accomodate ANY height differences, if you care to go that bother.

On the wide end, if you leave a 1/64 gap between boards, tapering down to tight. You will make that inch up in 64 rows. If you leave a 1/32, you will make up the inch in 32 rows.

Thats a great a cheat when you can use it, but I believe the OP is using a float floor, so most likely a uniclik or some other locking joint system which would allow for that spacing.

Darn

That changes everything. Thought I was being slick!

Have the off wall, on the side that has stuff set on the floor. You never notice it!!

Well, glad you were able to see past my typo, which indicated that you could use that cheat, instead of what I meant to say. Dang, leaving out one word sure can change the meaning of a sentence