Under account permissions (Manage [your account] > Permissions - there's a dropdown for "Create Applications", which can be set to either "Create" or "No".
The "Create" setting would allow you to create new apps.
The dropdown for "Account Permissions" has the following values: Full Management, Support-Level, No.
"Support-Level" would allow you to add users, manage apps, etc. - but will not allow you access to billing.
Note - if you give yourself "Support-Level" permissions, you would also NOT be able to change your Account Permissions anymore. So make sure that there's still someone else with Full Management rights.
Here's the online help for setting account permissions:
http://www.quickbase.com/user-assistance/Default.html#account_permissions.html
