If you haven't already found someone to do this for you, I'm a student from Norway looking for projects just like this one! I have good knowledge of PHP and MySQL, I can do this in a couple of days.
I can accomplish this by using PHP. I will be using cookies for the Splash screen and combined sessions/cookies for the vBulletin funtionality. This is not doable in simple HTML/CSS
Contact me through one of the following methods if you want to start working together!
Skype - Andodo007
Google Talk - aban0809
E-Mail/MSN - email@example.com
PM here on CodingForums
I'm willing to provide even more funtionality for your website if you want,
Looking forward to hearing back from you