I think it is perfectly understandable that people are going to assume you're mass/illegal file trading when you associate the word "download" with a program that is not for downloading files. The policy on this board says help is not to be given to people who wish to use the information for illegal purposes such as illegally file trading - and quite rightly so. Due to the obscenely large amount of people that come here complacently using words like "how do I get movies" and "how do I download with this?", it is hard to assume when someone says their going to a website and starting to download large files that it's perfectly legal.
Now, what has downloading from a website got to do with IRC/mIRC anyway? The only websites I know of that provide irc:// links to download files is packetnews/ircspy - both of which provide illegal file links.
Furthermore, trailers/demos can, within law, only be distributed by the makers/creators/authors of said trailers/demos - I don't know of a company that would release them on IRC with irc:// links...it's like Microsoft have demo games (i.e. Zoo Tycoon) - they release them from their website. Every movie trailer I've witnessed uses Windows Media Player or Internet Explorer to play, most websites don't make people download the trailer simply because it's less convenient. Your wording also implies you're regularly downloading files...how many people constantly download demos/trailers off of websites that use irc:// links to legally distribute their own creations over IRC? Not many I'd wager.
Now, The_Game suggested you use the search feature, and the reason for that is, people have issues with DCC all the time so using that is your best bet to see if others problems will help you. This forum is a bit like a library, use it as a reference and then write a new book if the problem doesn't already exist.
By the way, please do not cross post. It causes confusion and irritation to people, which is completely unnecessary. If you post in one forum, someone will answer your post as soon as possible
(For the interest of others, the other thread started is here
I too would suggest using the search feature, aswell as explaining exactly what downloading from a legitimate website has to do with mIRC (i.e. does it use irc:// links as aforementioned). It's important to keep in mind that the DCC protocol and mIRC were never built to handle very large files on a continuous basis. If you're downloading say 3 400MB files, then try and release the load a little.