[NiteWave]

I meant you don't need install plesk at all, litespeed + vBulletin will work well. since you do need Plesk, so Plesk + trial license litespeed + vBulettin will be the easiest way to go.

usually, user setup Plesk + apache + app and make them working, then install litespeed which will read and parse apache's httpd.conf, build lsphp, then stop apache and start litespeed. all virtual hosts configuration are through Plesk + apache.

this wiki page is for the detail steps:
http://www.litespeedtech.com/support...i:apache:plesk
How to replace Apache with LiteSpeed when used with Plesk