Quick Tip - iFrames
Level 100
First, what is an iFrame? iFrame means "inline frame", which MSDN says: "The IFRAME element functions as a document within a document, or like a floating FRAME. The frames collection provides access to the contents of an IFRAME. Use the frames collection to read or write to elements contained in an IFRAME."
So in CRM v3 Microsoft provides the ability to embed iFrames into MSCRM forms. Since an iFrame is just an HTTP link, you can embed virtually any web link into the iFrame, be it http://www.msn.com, http://search.msn.com, or a custom application you created such as http://localhost/mycustomapp/app.aspx. To make this feature even more powerful, MSCRM gives you the ability to pass CRM object values to the iFrame. So let's add an iFrame to the Account form.
Step 1. Determine the URL of the web page you want to load in MSCRM, this can be as simple as http://www.msn.com or whatever. The easiest way to do this is to load the app in IE and simply copy the URL from the location bar. I am going to show and example of a custom app on my machine which allows an MSCRM user to upload a document to Sharepoint. The application URL is http://crmserver/stsupload/upload.aspx

Step 2: Open MSCRM and Click Settings->Customizations->Customize Entities->Double-Click the Account Object->Click Forms and Views->Double-Click "Form"

Click "Add a Tab", name it iFrame,, then click "Add a
Section", name it "iFrame", make sure that section is highlighted, and click
"Add an IFRAME"
The first page you'll see is shown below. Type a name for your iFrame and use a URL you know works, like http://www.msn.com

Next, click the "Formatting" tab and check the "Automatically expand to use available space" box, click "OK".

Back at the form, click "Preview->Create Form"

Click your "iFrame" tab and you'll see MSN.com loaded inside your iFrame.

Expand the window and the iFrame will automatically expand to fill the space.

Close the form to get back to the customization panel. Click the iFrame and Select "Change Properties"

Change the URL to a different URL, I changed it to my custom app, and click Preview->Create Form again. We see our custom application in the iFrame.

And that's it. Next, we will create a custom .NET application that reads the MSCRM object variables we can pass to the iFrame.