How to put a program in system tray?

Tray It!

Tray It! is free and seems to work fine on Windows 7 32bit; there are some issues on Windows 7 64bit.

So far I am impressed with "4t Tray Minimizer" (and I am using it on 64-bit Windows 7.) Good wizard to get you started too.

The comments in eXtra Buttons suggest several people have had trouble with it.

I think you will need a 3rd party application to do this. A Google search for "run in system tray utility" returned several results. (mostly shareware, not freeware).

As an aside, that area is correctly called the notification area, not the tray. http://blogs.msdn.com/oldnewthing/archive/2003/09/10/54831.aspx