BEST METHOD FOR BOOK MARKING:
Before you read how to add a single "Make this page my Home Page" button (bookmarking for IE and FF), I strongly suggest that you use the code from AddThis. It enables many bookmarking features, and is the easiest and most reliable. ADDTHIS.COM IS THE BEST WAY TO GO.


IF YOU DON'T WANT TO USE ADDTHIS.COM, HERE IS THE CODE. SORRY, THIS CODE ONLY WORKS IN IE. SEE FIREFOX SUGGESTION, BELOW.
This code can be added to your Ning Network via a text box, page, or custom coding. You should be able to add this code, and when your members click on the link, it will make your Ning Network their HOME PAGE.

Be sure to do the following:

• Replace http://YOURWEBSITE.ning.com WITH your Ning Network URL.
• Replace the link text with your text: Make XXXX Your Home Page.
• I made the font size 75% of the regular font size. Just remove style="font-size:.75em;" , if you don't want to adjust the font size.

CODE:
<!-- coded by: Jen of http://theningdirectory.ning.com/ -->

<a style="font-size:.75em;" onclick="this.style.behavior='url(#default#homepage)';this.setHomePage('http://YOURWEBSITE.ning.com');" href="\">Make XXXX Your Home Page</a>

You cannot add this code where Ning strips the code, like in this box. I tested it in a text box, and it works fine.
============= FIREFOX AND IE SUGGESTION ==============
FireFox and IE Bookmark Code

I did not test this. This is not for someone who has little experience in coding.

Apparently this is not easily found or done for FireFox. The site called Dynamic Drive is one of the most reliable sites, online. They offer the code. It will take up a lot of space in your Analytics Box. Here's the link for code and instructions:
FireFox and IE Bookmark Code