Here's a link to BB Code in vBulletin, but remember not all of the functions work in every forum:
BB Code List - vBulletin Community Forum
The bottom right quote link will bring up the reply with the other person's text quoted in it. When you click that link, it'll bring up their response, and there will be a little bit of code at the start that says, for example, quote=John Doe;1902985 with these brackets [] around it. That opens up the quote. Using /quote with [] around it closes it off. You can break up someone's responses into sections using these two functions over again, and type your own message in between. I'll try to give an example using {} instead of []:
{quote=yakimaboomer;15994}Things that quoted person said{/quote} Then you can type all the bits you want to, and you can reopen it again with {QUOTE=yakimaboomer;15994}more stuff that quoted person has said{/quote} and close it off again.
I hope that helps.... I'm not overly savvy with that. If you try it out, click the preview button alot.... it'll tell you how you're doing *g*