This topic was discussed in another thread... I'll find it and post the URL shortly.
Yes ....I would wrap the two different parts that each user has to fill out in a subform and then create a scripting function to lock all fields in a given subform. I have included a sample that will show you the scripting object to do the locking. In this case it is locking the entire form, but if you pass in the subform that you want to lock then it will only lock the fields below the subform. The code to call the scripting obejct is behind the lclick event of the lock fields button. In my case I am passing in form1 (which is the root node of the form).