Adding named instance to existing a/p setup

Hi all,
I have a sql 2005 a/p cluster with default instance up and running.
How to install an additional named instance ?
- I have an additional cluster name/ip
- have added an additional cluster resource group
-> but during setup this additional cluster group is not recognized ??
-> do I have to add additional SAN volumes (and resources) for my named instance ?? (and put them in my new cluster group)
Thx for a hint
acki

As a clearification of the above question is the following true:
for each instance of mssql server 2005 in a a/p scenario you need it's own:
- cluster group
- virtual name/ip
- san disks
Thx for your support
acki4711