My recollection is that we get DW some time right after lvl 10... I think all preditors can DW.
A couple of additional points about poisons...
1) As stated above, each application lasts 12 hours -or- 200 procs - whichever comes first.
2) As soon as LU19 goes live, poisons (along with potions) will return to your buff bar without re-application after character death.
3) There are 3 different "classes" of poison. These are damage, stun & de-buff. You can apply one of each class but not more than one of any one class at any one time.
4) Applying poison adds the proc to all of your weapons, so with one application you get the benefit on both blades and your bow.
5) If a damage poison procs a second time while the first proc is still in effect, (and it happens a lot!), the 2nd proc will over-write the 1st. For this reason, I prefer a poison with a large front end, (initial damage), and a small DoT. That way, all I lose is whatever is left of the small DoT and the 2nd proc starts off with another big pop!
Welcome aboard and good luck, Ranger!