Zahid,
It is in the Windows Design Guidelines, I don't have the spec in front of me at the moment or I'd post a reference. Blinking text is extremely hard to read. The "proper" way to alert users is to flash the titlebar. The API call to do this has been posted in other threads here.
>I hear comments like this a lot. It's been a while since I read the Windows standards, but I don't remember them specifically prohibiting blinking text. Did I miss it? Or do you mean, "Blinking text is non-standard"?