Query/Loop for Both Random and Fixed Blog Post Order

Hi all

I am developing a wordpress blog for a friend and he’s asked if it’s possible to have all his posts shown in a random order.

However, he would like an exclusion to this rule.

If a post has a specific tag (standard tag; not a custom field), that post is shown first and then the remainder of the posts are randomised.

I can fix posts and randomise them – but I’m not sure how to do both within WP.

Can anyone help please?

Thanks Anes