To add to what Aron said:
Bit rate determines how compressed the file is. While it does effect sound quality, it does so in the way of a parabola (higher the bit rate, the less difference you will see).
Sample rate is the quality of the recording itself. It has much more of an effect on sound quality as it is directly related.
What have you been using for conversions, and how have you been converting?
Michael: Jodie, how's my schedule look for today? Jodie: You've got a conference and dinner party at the Japanese Embassy regarding wildlife protection. Michael: Oh, yeah...sorry, but I'll have to cancel that. I'm heading out to save America!