You could probably alter the JavaScript post back on the Forms Library
page. If you wanted it for every Forms Library you could alter the
SCHEMA.XML.

Can you please suggest some steps how to do that ??

Look at the JavaScript that gets executed when you click on the InfoPath
form in the form  Library. See if you can alter it to pass the
information that you need.

Beyond that, I'd have to research it and I don't even have SharePoint
installed on my box right now. But I'll bet it could be done.

Actually I want to know the current username .

Through javascript by " wscript.network " we are able to get current
system login username, but I want current context's username(i.e system
login is for ex : localadmin login and user open's sharepoint  site
using dom\username account and he opens infopath  form , in that infopath
form I need dom\username not local userlogin )