FFT / IFFT sample rate converter

I am currently writing a FFT / IFFT based sample rate converter. However,
after finding some code to do the transform (both fast and accurately), I
am stuck.... the code I am using for the transform is from
http://local.wasp.uwa.edu.au/~pbourke/miscellaneous/dft/. When I try and
enlarge my buffers up to their final size, I hit the problem of the output
is not the same as the input (in the way of the sound that is output, not
by the fact I've tried expanding the buffers). My code is written in C and
is to convert from an arbitrary rate (in my test case it's from 8363Hz) to
44.1kHz.

I am in need of some desperate help as this code is what a software mixer
I am writing depends upon for converting samples to the appropriate rate
for proper mixing.

If posting my code will help, then I will, however it is a long excerpt.

Thank you in advance for anything you can tell me that might be able to
help me.