Custom logout redirects

With Drupal 5.7 adapt then use the following link:

http://www.example.com/logout&destination=node/mylogoutpage

This link do a log out then redirect to the page "mylogoutpage".

On your site, replace "www.example.com" with your domain and change the "node/mylogoutpage" with the path of your goodbye page.

If you use menus disable the default "logout" link in Admin --> Menus and then manually create a link somewhere on your site that uses the above link.

Source: http://drupal.org/node/120253

This feature doesn't accept third party urls. I'd like to do something like:
http://www.example.com/logout?destination=http://www.another-site.com/?v...

Possible? when I try that example on my site, It just goes to http://www.example.com/www.another-site...etc

Any ideas?
Thanks!

modify the drupal_goto() function!

Thanks sid. I'll have a look.

One more question, if you don't mind:
Is there a way to set up a custom logout? Not my altering core, but maybe in template.php or something?

I'd like to do a bit of php code during the logout process. My install ties into a custom login process, and when a user clicks a logout link, I have to do a couple of database calls, update a few session variables in addition to logging out of drupal.

Any way to have a custom function somewhere, where I could do something like this, without altering core?
TIA

please check the links below.
http://drupal.org/node/203538
http://drupal.org/node/120253