Wasim - there are some good solutions listed on the Mercury CSO KB about sending mail from WinRunner.
Depending on your settings for Outlook (security settings and such) it may not be the easiest thing to do and you might have better luck through straight SMTP or via the CDO.Message object.
Also look into running WinRunner from the command line (Chapter 26 in the User's Guide I think), that way you can set up a scheduled task to launch WinRunner to send it out.
Although - is this e-mail specifically tied to WinRunner? meaning is the e-mail realted to a test of yours that is running otherwise or are you just using a $6000 application to send out an e-mail which you could do from VBScript or PERL?