As I was about to write a post about Using the Auto Mapping Feature I realized that a similar post was available at the Microsoft Dynamics CRM Team Blog. Their post is very complete so I thought I should add just an important warning.
When you create the CSV file you'll use to import the data to MS Dynamics CRM 4.0 remember that the field names are case sensitive: "E-mail" (correct) is different from "E-Mail" (wrong). I lost a couple of minutes to fix my data files in order to use the Auto Mapping Feature because of incorrect field names. If your pick list values (file) are equal to CRM's picklist values you can also use the Auto Mapping feature.
If you can't get it right or if your data type needs some kind of transformation (for instance pick list value "Done" becomes "Completed") and you prefer not to mess with your data file then you'll have to create your own Data Map. I will write about this tomorrow because although it's simple I had to use a workaround to accomplish it.