I need to generate random numbers from Binomial(n,p) distribution.
A Binomial(n,p) random variable is sum of n uniform variables which take 1 with probability p. In
If you are willing to pay, then take a look at NMath by Centerspace.
Otherwise, the C code used by the Stats program R is here, and should be straightforward to port to C#.
EDIT: There are details (inc. code) on creating a method for this on p178 of Practical Numerical Methods with C# by Jack Xu.
ANOTHER EDIT: A free C# library that does what you want.