DOCBOOK-APPS: Making sure headers in tables are not too close to therule beside them

Hi,

I am noticing that my tables look ugly, because the elements in them are
hard up against the left margin rule. 

How can I ensure that there is some space there?

Regards
-------
Richard Sharpe, 
Samba (Team member, www.samba.org), Ethereal (Team member, www.ethereal.com)
Contributing author, SAMS Teach Yourself Samba in 24 Hours
Author, Special Edition, Using Samba