I want to use a dc power jack in my circuit, and I chose this. After eagle does not have this schematic, I have to draw it on my own. Unfortunately I do not understand the pad size dimensions. It tells me that it should have the dimensions "4-3.0x2.0". Which size does that mean? In eagle I have the option to use the size "3.81x1.9304", which sounds as the best variant. Is that correct?
You should definitely use the exact nominal pad dimensions and spacings shown on the datasheet. You might have to set the grid differently or something like that on Eagle (not a user) but I'm sure you can do it. See any tutorial on creating SMT parts from scratch.
Presumably you're going to use two 2mm holes for the location posts (even though one of the posts is actually designed to fit a 1.6mm x 2mm elliptical shape (probably about 1.3 x 1.7mm). I would suggest you specify those holes as unplated so the pins fit nicely. You might even make them a touch smaller than recommended if you're using hand assembly. The unplated designation may result in a slight cost increase in the PCB because it requires an extra process step. Sometimes folks nail down the connector with a bit of epoxy to make it more sturdy (eg. the SMT mini-USB connector on the Beagleboard).
As others have said, the through-hole connectors are much more sturdy than the SMT ones (even with the location posts), but it's better if you can use drilled slots for the tabs. Large holes work okay for hand soldering, but they suck up a lot of solder.