Tom Ogilvy wrote:
http://www.j-walk.com/ss/excel

on the left should be links to John Walkenbach's books. His power
programming series should be good for inside Excel. Also Stephen Bullen's
books:
http://www.oaltd.co.uk/Excel/Default.htm

Books are the last two entries on the left.
Will have a look.
Thanks a lot!
Volker