just go to
www.youtube.com , signup for a new account and after ur done, just login and press the button "upload video" , then it will open a page where there is a browse button so u can select the video you have on your computer, after selecting the path of the video, just press upload and you should be able to see a progress bar indicating how many bytes you have uploaded so far, keep the page open until the progress bar reaches the end and it will AUTOMATICALLY opens another page (actually in the same page) and it will give you the links for the video, after you got the link (sth like
http://youtube.com/watch?v=cLgu8Ckb3LQ) , now you want to post it on the forum in a reply so under the replysection go advanced and press the icon labeled "youtube", and there enter the link in the box , and everything should work fine :)
ps: dont put in the box the full link,ex :
if this is the full link of the video:
http://www.youtube.com/watch?v=Y4ktvNztwsY
put just after the = (ie: Y4ktvNztwsY) in the box.
if you have any troubles let me know . . . cheers !