Mapping will avoid some of the pitfalls of masking, such as hidden link URLs.  Here's how to MAP using GoDaddy and TypePad: 

First register the Domain Name at GoDaddy.  Leave GoDaddy running in one Browser window or tab. 

Go to TypePad in a different browser window or tab

Hit Typepad Control Panel -> Site Access -> Domain Mapping

Click "Begin Here: Map a Domain Name"

Type in the new domain name, click Get DNS Settings. Typepad will display the CNAME Record,  you can drag your curser across the CNAME and hit Edit -> Copy, so you don't have to type it when you get to that step.... then Click "Complete Final Step"

Tell Typepad which individual blog to map, click Add Domain

Now back to GoDaddy

At the GoDaddy Domain Control Center, place a check mark at the left of your new domain to select it, then click Nameservers

In the Default Nameserver tab, select "Default Parked Nameservers", click OK

 In the section below, double click the domain name to go to the details page

Find "Total DNS" in the middle column, and click on "Total DNS Control and MX Records"

The first row item in the list is www @

Click on the pencil icon (edit) in the far left column

On the line "Points to Host Name" type  in the CNAME information from Typepad (If you copied it earlier from TypePad, just hit Edit -> Paste)  Click OK.

Wait.  This one took just about one hour to resolve.  Test.   When the domain address finally resolves to your TypePad blog, go back to your TypePad Control Panel  (Control Panel -> Site Access -> Domain Mapping)

Scroll down to the list of your domains.  Check your new domain "Active".  Click "Set"

And Brian, since your blog already exists, and you'll need to first disable your existing forwarding, you might want to do this at, say, 3:00 AM.