Dufwer,
I wrote a computer program that performed such calculations a year ago. I remember the derivation requiring some A Level Maths knowledge:
The sin rule: A / Sin a = B / Sin b = C / Sin c
And the cosine rule: A^2 = B^2 + C^2 - 2BC Cos A
If I find the code tonight at home, and nobody beats me to it, I'll post the formula on here.