When your making your reply just scroll down the page and you can see all the posts before yours. Just copy and paste up to your reply box and put this around it: (replace XXXXX with username of original poster)
"[Qu ote=XXXXX] (Insert what you copy and pasted here) [/Quote]"
^ Don't put a space between the u and o I had to do that so it wouldn't literally quote the whole thing lol.
If the quote you want is not listed on the bottom of the reply page, because it is a page or more back, there is a link you can click at the very bottom of the page that will open a new window at the first page of the thread and you have to just find it a copy and paste it.
Some forums have multi-quote options to make it a lot easier.....hint hint....