Have you solved this problem yet?  I am trying to do the same thing and find that the manual is not very helpful.
Would love to know if you found the answer.  If I do I will let you know.

Glad to know I'm not the only one out there that needs to know how to do this.  

FYI I am running Complete Accounting version 8.

Thanks

Haven't found an answer yet.  I'm still recording commissions manually.
Do you use Crystal Reports?  I am thinking about adding it to our system in hopes that it will allow a report to be written using any field.  Maybe with this I can separate the sales amount from the freight amount.

try asking here:
http://www.peachtreeusers.com
good luck

Answer to commission sales issue.  Whether or not an item is commission vs. non-commission is determined in inventory setup.  There is a box at the bottom of the inventory setup window where you check mark if it is commission item.  
When you run the sls rep. report the total sales amount in the commission column is equal to the sales amount of all inventory items that were check marked during the item setup.  Non-commission will include all others (freight, inventory items not checked, etc).