I just added my newsletter sign up box to my various "facebook fan pages" and here is how I did it:
1. Go to the application "FBML"
Click on "add to my page"
2. A box appears titled "Add Static FBML to your Page"
Click on as many or as few of your fan pages you want to add this box too...(btw...you can also add several of these FBML boxes to EACH fan page so you can put multiple widgets, etc...onto your page)
3. In facebook, go to your "pages" area.
Click on your fan page. On your home page, just under your avatar picture, you will click on "edit page".
You will be taken to a list off all of the applications you have working on your page. Scroll down until you see the "FBML" box.
Click on the pencil to edit.
4. In a separate window, log into whatever newsletter service you use (bravenet, vertical response, cc) and obtain the coding for your specific box.
Copy the coding.
Back in the edit box for your "FBML" box, come up with a name you want to use: "Newsletter Sign Up" or whatever you want. Then, in the large box, you can paste that newsletter coding right there.
(***hint: I played around with the "width"...It seemed to me that a width of 185 or 190px worked well)
Click on save.
5. Go back to your fan page home page. To make it easier for your fans to find the form, you can add it as a navigation tab. Just click the "+" icon in the top navigation list, and select your new form from the list.
**You have two options of what to do with the newsletter box. You can leave it at the top OR you can also add that box to your sidebar if you prefer!
Now your facebook fans can sign up for news as well, all in one place!
How to add additional FBML boxes to your fan page::
(Above, I mentioned that you can add multiple FBML boxes to your fan page. You can.)
-To add additional boxes, go back to that "edit page" link that is just under your avatar photo.
-Scroll down to the FBML application again and click on "edit". Your box will come up.
-Scroll all the way down to where you see "add another FBML box". Click on that and you are on your way to adding another!