Hi Peter,
It's really depends how it looks structure or your audit system. If audit log is using other entity you will need to have a relationship between then. In this case you ca use workflow are refer to this record. I have audit with custom entity (called Audit) but in the one record I'm storing all information (entity name, old value, new value, who create it and when) like here:
http://crmaudit.codeplex.com/In my case it's not a problem to create a workflow equals with your requirements.
Trigger: When field will be changed and mark all fields which are in form
Actions: Send email and in body I need to put values from Related entity (to see it you will need 1-N relationship between them) and I'm able to put all information.
If your case you have 2 records (one for old value and one for new - which is very weird) I don't have see posibility to do which by workflow unless it will be a custom workflow which requires development.
My Dynamics CRM Blog:
http://bovoweb.blogspot.com
