drop your style folder in forum/images/styles on your ftp
[you may need to create the folder styles]
import the style.xml via admincp - styles & templates - download/upload styles - import style.xml
choose your style.xml as the source [browse the folder on your pc for the .xml file from the style package you downloaded]
create new style [yes]
ignore style version [yes]
Give it a title
Parent Style [No]
Display order [doesn't matter, lets say 3]
Allow user selection [choose yes if you want users to be able to choose it as soon as you finish installing]
click import you're done, you will need to add your banner, you can either upload it to forum/images/styles/*yourstyle*/misc/*yourbanner.gif*
or you can upload it elsewhere and add the link to admincp - style manager - *yourstyle* - stylevars - title image
edit - when i started posting this you hadn't had a reply lol, oh well it's there now