Mark,

You can use the set item permissions action to change the permissions for a particular person (such as the person who created the item) or for a particular group to whatever permission set is needed.  In your case, you could set it to read only or view only which should help you out.

Be careful on changing permissions to individual items to ensure that this is the correct and best route to manage permissions by.  There is nothing like having to go back into a big library and edit permissions on individual items.  You may want to change permissions at a group level and manage the groups easier.

Thanks Eric!

This was really helpful! I was initially looking at the Form settings, when I should have been looking at the Workflow (:

Mark,

Glad to assist.  Keep using the product.  You'll get the hang of it quickly.

Also, if you're somewhat new to the platform, check out my post here - Nintex Hangout on the Nintex Ebook Nintex Hangout - Live from Melbourne (Mar 16th) - Google+