How to link an existing .exe to a DLL?

[babygal]

I have created a project, executable called, app.exe.
Then another project, executable called, proj.dll, together with proj.lib and few other header files.
How do I link my first project, app.exe to the proj.dll?
What are the step by step details and configuration settings I am required to do, so that both the projects
can be linked successfully?

I'm doing programming for Windows platform, and using Qt 4.6.2 and Qt Creator 1.3.1.

Please help.