So you want the form in the child window to submit to a different page and then return to the parent or child window? Without lots of complex JavaScript-related shenanigans, this is pretty easy to do with ASP. When you open the child window from the parent, pass the URL of the parent window to it. Store this as a hidden form variable in the child window's form.
The child window's form should have action="" set to whatever page you wish to submit to and importantly, target="_parent". When you submit to the other page, do all your database processing and then Response.Redirect to the submitted URL form variable, which will then reload the parent page again in the parent window.
I'll leave closing the child window when you submit it, down to you. It's not that difficult; you need to wrap a JavaScript handler around the onSubmit event for the form which executes window.close() after calling form.Submit().