can u add groups to the button?
<attribute name="groups">base.group_sale_manager</attribute>​

Yes Omar. You can do this by doing the following:

1. Create a new Security Group to be used to control access to the confirm button

2. Assign the new group to the users who should be able to access the confirm button

3. Customize the Quotation/Sales Order form view using inheritance and add a groups attribute with the new security group to the confirm button. 

Try this in your xml file... <field name="name" groups="base.group_userB"/>. Now the userB group only can view the field....