different template depending on domain / url

One wordpress installation on main domain, then have some other domains point to it, show same data but a different template?

This should work.
Basically you want to use the same database on more than one website.
My solution:
1. Install WordPress on domain A, using database D1 and add content.
2. Install WordPress on domain B, using database D2.
3. Change the wp-config.php file on domain B to use database D1.
Done.

ah ok, yer that sounds good.

however id want to manage all of them from domain a

so id log into domain a’s wp-admin, update and add bits and bobs, which appears on all the sites

I think you could do it with the new Multisite features of WordPress 3.0 combined with some modified themes.

define('WP_ALLOW_MULTISITE', true);

You should modify the themes so that all of them get the content from the same blog.

Check these out:

1. https://codex.www.ads-software.com/Create_A_Network
2. https://codex.www.ads-software.com/Migrating_Multiple_Blogs_into_WordPress_3.0_Multisite