4 parameter logistics - GraphPad

Hi guys

Dont know mutch about statistics and i thought some of you might be able to help.

I am doing research ELISA (I am a medical doctor) and the kit manufacturer says on the manual that i should do 4 parameter logistic analysis of the results i get. I am using GraphPad Prism 4 for the statistics and i cant find anywhere this type of analysis - it simply isnt there.

The data type are simple and straight forward, meaning i get some optical density values from samples of known concentration and from that i interpolate to find the values of samples of unknown concentration (cytokines). Up to now i was using linear regression for getting the values, but according to the manufacturer this is not the correct way to process the data.

I know it belongs in the non linear category (i think) but its not in the drop down menu of available analysis. Does it have any other name (synonym) or is there a specific equation that i can fill in in custom analysis? And if there is one, there are also some A,B,C,D values i have to fill in that i dont know anything about.

I can also use SPSS for the data analysis, but i am not sure whether that choice will be available plus i will have to learn to use the program from scratch.

So basically i have 2 questions:

1. Do i really have to do 4 parameter logistics or linear regression is also fine (the values i get are copmpletely different).
2. Where is the 4 parameter option in GraphPad Prism?

Can you guys please help me? TIA