How to make 2 application to run at a time

Question

Hi

In my dot.net application

I have an Mail application in which by giving username and password enable the user to enter in to their email inbox.

I have another Userapplication in which user need to register by giving email id as unique key.(this email id + password is given above to enter into the mail application).
.
now the thing i need is

i need to get this 2 application to run in same time.that's in the "userapplication" when they login into the sire  i want the user's unread message count to be shown in home page of the user.

how to make this to get display..

Thanks