I wan to give an associated partner access to 1 account ( and only 1 accounr) in our CRM system

I wan to give an associated partner access to 1 account ( and only 1 accounr) in our CRM system

Hello,
I have recently setup the trial enterprise edition ( moving over from Infoathand)
I have to say I am very impressed so far.

Here's a question: I set up a type of User 'Partner'. There are external consultants. I set up an account and assigned him 'partner' usage.

I want this user - when he logs in - just to see all information relating to 1 account and no other.

How do I do this?
Regards
Dermot Foley
Dublin
Ireland