How do I add a custom object to a standard Lookup type field?

When logging a call, when I want to choose the name of my contact, it only points to Contacts and Leads. Can I point to a Custome Object?

Is there a way to setup email alerts when a field in Tasks change? I dont have the set E-mail Alert option when I try to add a workflow step for the TASKS object

SFDC support person directed me to developers as the only workaround is to use apex trigger which deals with constructing codes to make it work.

Can anyone help me?