To refresh your math maybe you can check out some of the Schaum books, which are cheap. Depending on how much you need to refresh, you will need some of the following: Elementary Algebra, Intermediate Algebra, Trigonometry, Geometry, PreCalculus.
Then you can start with calculus. If you are refreshing calculus you can get the Schaum book too. If you do not know any calculus then you will need something more substantial. There is Kline's book, also cheap but excellent; if you want to supplement it with problems there are the Schaum books again. If you want a more rigorous calculus book there is Courant and John's "Introduction to Analysis, Vol 1".
With that math background you can start to study physics. The book Phyisab**** recommended, Serwat and Jewett, is a standard book, but I have not read it myself. Another book to look at, which I think is excellent, is Alonso and Finn. I have an old copy I bought for cheap ($2, I think, at a 2nd hand book store!); the new book is expensive on amazon.com (like all new books are...*sigh*) so try to find an older copy. By the way, books at this level usually have something to say about quantum mechanics and special relativity, but they are very, very elementary.
Then you will eventually have to learn more mathematics before you can continue in your study of physics, namely: vector calculus, ordinary differential equations, linear algebra, and more. But for now I think you have enough to read :D When you are done with that you can come back and ask where to proceed from there.
As Phyisab**** notes, there is some way to go before you can read books on quantum mechanics and relativity, never mind string theory! But this is where to start on that path to those subjects.
Good Luck!
