Rate() and PMT()

If you are familiar with Crystal reports or Visual basic, you may be familiar with the Rate and Pmt functions.

I need to duplicate them in SQL sever 7.

Anybody have code for this already? I hate re-inventing the wheel.

More (Unnecesary) details:
I have a client who has handed me the formula that I need to use for calculating Interest rates. Unfortunatly, the formula was written in Crystal reports, so now I need to pick it apart and do the work that CR does automaticly. Any help?Check this site, it should contain what you're looking for:

http://www.wheatworks.com/formula.htm