Question : Populate lookup field with data from parent site list

I have a toplevel SharePoint site with a list called 'Customers'.
I have 3 sub sites, called 'Sales', 'Projects' and 'Support'.

I would like to be able to make lists etc. on each subsite, with a lookup field for the 'Customers' list on the toplevel site.

How to achieve that - I'm open for all good ideas including programming it myself.

Answer : Populate lookup field with data from parent site list

http://www.sharepointblogs.com/dortiz/archive/2008/01/24/leveraging-the-use-of-site-columns-part-i.aspx