This works fine. 64 is for information icon and Ok button. But I not able to get rid of "vbscript:" which present at the start of the title. Not sure why it is like that.
<html> <head> <script type="text/vbscript"> Function myPopUp(test) MsgBox test, 64, "My Custom Title" End Function </script> </head> <body> This is my <a href="#" language="vbscript" onclick="myPopUp('How are you do today')">link</a> which you can click on for definition. </body> </html>