Creating a New My Sites or adding My Sites to a Moss Portal
The other day I had to add My Sites to a client Moss Site

Firstly create a My Sites Web Application
Central Administration > Application Management > SharePoint Web Application Management:
Create or extend Web application

Then create a My Site Host Site Collection
Central Administration > Application Management > SharePoint Site Management:
Create site collection
Remember to set the site template as Enterprise>My Site Host

Now add a managed path if you don’t plan to use Sites as your location
Central Administration > Application Management > SharePoint Web Application Management:
Define managed paths
Add your Location as a wildcard path.
Next go in to your SSP
User Profiles and My Sites: My Site settings
Change the
Personal Site Services: to your new Web Application
And change
Personal Site Location: to your new location you defined earlier

And there you have it a new My Sites.