[support] User permissions - limiting node or page access

[Luke]

Hello

I would like to have user X be able to edit content of a particular node, 
or page, or other entity.

There is talk of this here: http://drupal.org/node/5229

however, as noted in the last comment there (June, 2008), this issue has 
received no apparent action since 2004.

Now, it could be that this has been handled in some other way, but this 
level of permission granularity does not seem available in 5.7.

This is not a one-off: I have several "department heads", who need to be 
able to control their own pages, and only their own page(s).

Are there any current solutions for this for either 5.X or 6.X?

Thanks

Luke