Perhaps the best way of understanding String Theory without being bogged down in the mathematics is to understand the reason for it's existence.
Here is an introduction to String Theory in terms of the lead up theories
Special Relativity, General Relativity, Quantum Mechanics and Quantum Field Theory. The mathematics is only in passing. (Let the Physics and Applied Maths post grads do the suffering)
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A few good lines in the presentation, add gravity to Quantum Field Theory and you get a train wreck.
http://www.slimy.com/~steuard/resear...o/slide01.html
Hope this helps
Regards
Steven