Yes its possible, but i've only ever done it using an .exe that was written by Necroman, who is one of our Ops in #mIRC, its called mStealth, it may be available at www.mircscripts.org if not give me a holler and i'll mail it to you
ScoT #mIRC Undernet
Give a man a fish feed him for a day, Teach him to fish, feed him for life
Not that it's anything to do with me, but, why on earth would you want to hide mirc from the taskbar, from the tray and minimize, it, if i'm right that'd mean you couldnt even see mIRC running, which to me, sounds dodgy.
NoNameScript has an icon called Nothing.ico, I used it in college a lot when I was playing around on IRC (its a blank icon that doesn't appear in the tray) if you don't want that you could download something called iconic tray from download.com, however you need to keep installing it every 14 days.
What do you do at the end of the world? Are you busy? Will you save us?