It'd be appreciated if any of you could tell me who could I make text or an image appear upon connection to the website (Welcome, enjoy your stay) and disappear forever in 2 or 3 seconds after that, just to wish warm welcome to the people coming to the website without having to click on a button?
Many thanks in advance!
Why not just have some normal welcome text on your Home page?
That aside, you could have a top bar appear and disappear. An example is at http://www.girlsgogames.com/ there's a checkbox there, but in your case it's not asking a question so you'd just have it vanish after several seconds. I find this type of "popup" much less intrusive and they generally fit into a page design better. They can also be adapted to mobile layouts easier I think.