You want three types of materials.
1) Straight up review
2) Practice problems
3) Full length tests
For review, I used Kaplan, a lot of other people use Schaum's and Cliffs and their textbooks (you can search the forum to find people's opinions of each of the resources.)
For practice problems, Kaplan subject tests and Destroyer. (I've never actually used Destroyer, but it is the one with a million questions, right?) Again, search forums for people's opinions.
For full length tests, Topscore, Achiever and Crack. Topscore and Achiever are actually full tests, while Crack gives you full section tests for PAT and math, depending on what you buy. I only used Crack for PAT but I thought it was amazing, definitely the best practice out there.
And how much time you need depends on how much timer per day you put in, how productive you are, what science background you have, etc, etc, but if you're asking about a general range, I think if you have a solid science background and you're studying all day every day, about 6-8 weeks is average.
Good luck!