If you're asking what i think you are, you could use an equation:
Create the dimension you want to be govening and the one you want to be governed,
create a new equation -> tools\equations\add
click the governed dimension, type in the relation then click the governing dimension.
should end up...
eski1
http://cgi.ebay.co.uk/Solidworks-2005_W0QQitemZ7224646482QQcategoryZ96946QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
solidworks sometimes comes up on e-bay might be the cheapest option available but i couldnt tell you if it were the best.
id have said you can teach yourself the basics, if...