create the stored proc, with whatever parameters are needed, or none if you want (Crystal can filter, but I prefer the stored proc...use the power of your database server and the logic of sets to speed things along).
When you create a report, you select a connection and then a database and then you get to tables. Instead of tables, select Stored Procedures. Find the one that you wrote and select it. Now you can use it just like a table.
As for transfering the report to run from the stored procedure instead of the tables....
1) add the stored proc to the report as above.
2) for each field on the report, select the matching field from the stored proc, place it close by.
3) right click on the original field, select 'Format Painter'
4) click on the new field
5) delete the original field and move the new field into the same location.
6) repeat for all fields on the report.
Now for the fun part
7) check the original tables, if all of the checkmarks are gone, then go to the Database Expert and remove the table.
8) if checkmarks remain, start searching in formulas, Running totals, and Section Expert and replacing the old fields with the new fields...don't forget the Report/Selection Formulas as well.
Repeat 7 & 8 until all the tables are gone and all the remains is the stored proc.
You probably had parameters, update the new parameters created by Crystal to be passed to the stored proc with the verbiage in the old parameters, and you should be all set.
Keep a copy of the original report just for comparison.
Hopefully this is enough detail.