help with posting style profile

[cliff barnes]

Hello, I have two problems to solve with my Gnus program.

Problem 1:
I have in my .gnus file a line similar to this:
'((".*"

         (name "cliff barnes")
         (organization "Wentworth Oil" ))

However, although a Usenet posting will show the 'from' as 'cliff 
barnes', when the message is opened to be read, below the 'from' is a 
field called 'sender' - which actually shows the user name and host name 
of my pc!!

My question is how can I set this to a null value or even another name - 
without of course changing my unix user account name.

Problem 2:

I only read / post to 3 newsgroups. I want to maintain 3 different 
posting profiles for each group I post to. I would be grateful, if you 
can show me how to do this, by specifying in full- the newsgroup name.

eg

1. alt.music
        (name "singer")
(organization "record company"))

2. soc.culture.policy
(name "presidential")
(organization "white house"))

3. rec.arts.games
(name "fun")
(organization "cards"))


Can you show me the right wording to make each of these unique example 
profiles automatically kick in whenever i post to one of these 
newsgroups? Ideally, i would like the default "." to work if i posted to 
any group other than these three.

Am I trying to use posting styles for something its not set up for???
I'm not sure at all :(
Thanks for reading and any help you can give me.