you can't just use the stylesheet from the home page cause it doesn't use the same classes/ID's found on the forum stylesheet...
I suggest editing your forum styles via the STYLE MANAGER - you can enter the same settings from that of the home page stylesheet.
http://www.vbulletin.com/docs/html/stylemanager_css
I recommend adding a new style (duplicate) for testing purpose.
http://www.vbulletin.com/docs/html/s..._add_new_style