The stretch from the end of the Paulinskill Valley Trail, to the Water Gap, I have not found much on-line about it. Here is the way I took and seems the best possible, at about 8 miles. This was from June 2010.
Last part of Paulinskill Valley Trail had a very muddy, almost impassable section, this was shortly after the last "train station" with telegraph office. Soon after this it joins a driveway, to the left posted no trespassing but veering right is ok. Further down the road is a sign on left (facing other direction) for the Paulinskill Trail and past that is this leads to the end of trail at a gate with "Private Property" signs (also next to it is a sign for a "One Lane Bridge") at Bruglers Road.
Continue by making a left onto Brugler Road (south). By the maps above it looks like the old railroad continued on the right, but that is private land now. At end of Brugler Road make a right onto Warrington Road. Then soon after make a left onto gravel road for Columbia Lake (it looks like this may have been part of railroad too? but maps do not show it as such).
Continue on this until the end where you make a left where it goes under 80 through a tunnel. Soon after the tunnel is a dam on the right. Soon after dam the path forks, the one on right continues on elevated ground but eventually peters out. So take left fork which goes down eventually leading closely by a residence back yard before ending up on 46. 46 is now a divided highway at this point. Make a right on 46 (passing driveway of mentioned residence).
Cross bridge over the Paulinskill and cross 46 to get on side street (Washington Street) that follows the Columbia. I do not think there is a sign marking the street at this point as the street is merging with 46. Follow Washington Street for a few blocks making a left on Green Street to cross the Portland Columbia Pedestrian Bridge
. Look at message board there and you will see that you are at the current end of the Liberty Water Gap Trail! (Go down the hill for a beautiful view of the river and the house on the rocks.)
From here, 611 (North Delaware Avenue) is more direct but I preferred crossing 611 here to get on Delaware Avenue) (slight right). Take this North. Take note of the beautiful architecture on the left. Later this crosses 611 again (before it does it changes its name to Church Street), this time take the smaller road on the east side called Slateford Road (an old slate quarry). When this crosses 611 again you are in the Delaware Water Gap National Recreation Area. Continue North on 611.
I think its about 4 miles to the AT trail and toll gate for I-80 Delaware Water Gap bridge. There are 3 rest stops on the way but they do not offer facilities, just parking lots with spectacular views of the Gap