You want to use vBulletin's 'Stylevars', if you are running vb4. I will toss you some reference links to get you started. Make sure you are using one of the later versions of vb4 as the stylevar system was not finished in the early versions.
Basic:
http://www.vbulletin.com/docs/html?m...rsion=40201500
https://vborg.vbsupport.ru/showthread.php?t=256370
http://www.vbulletin.com/vbcms/conte...-10-Easy-Steps
More Advanced:
https://vborg.vbsupport.ru/showthread.php?t=230309
More Advanced - Videos:
http://www.youtube.com/watch?v=sfwle1enLms