I find any site that plays sounds like this rather annoying. Nothing worst then browsing at 3 am and waking everyone in the house up because I forgot to turn down my speakers. It will also cause slower browsing for your dial-up users with the inital load.
The only method I know of outside of flash would be using javascript. Here is a page that deals with this subject:
http://www.theopensourcery.com/jsounds.htm
If you know your way around the template it shouldn't be much work to get this working within vBulletin. If you need help let me know.