Is it possible to make a tab or window blink on demand with Java or HTML or ASP/php?

Similar to how applications that don’t have focus will flash their tab on the start bar when they want your attention. Is it possible to cause an internet tab or window (if you don’t do tabbed browsing) flash itself like this to get the user’s attention?

Or to put it another way: What normally triggers that to happen on an internet page.

I don’t need it to flash when it IS focused. I just want to trigger it so that a page will alert the user if it wants their attention.

I believe using a Javascript alert() box will accomplish that.