Is it possible to change the default email address when sending emails from a certain custom object?  Right now, the default is the user who is logged in but I'd like to change it to an org-wide address but only on a particular custom object.

I want to trigger a workflow every time a record is updated.  I used this formula from SF: 

https://help.salesforce.com/apex/HTViewSolution?id=98335&language=en

It works, bu the problem is that it triggers both when the record is created AND when it's edited.  I only want it to trigger when the record is edited.  How can I exclude records that are being created?

I want to trigger a workflow every time a record is updated.  I used this formula from SF: 

https://help.salesforce.com/apex/HTViewSolution?id=98335&language=en

It works, bu the problem is that it triggers both when the record is created AND when it's edited.  I only want it to trigger when the record is edited.  How can I exclude records that are being created?