You will need to know some simple html for this tip.
1) Start off by creating a group and name it "Classifieds". Then be sure to check off the boxes like I have pictured here (After completion). At this point put a check in the "Comments" & "Discussion Forum" boxes.
Note! I unchecked the Forum box so the forums will not be visible. (...but you'll still have the forum. You just have to link to it... via step 5)
2) Then I'm showing the latest posts via RSS Feed.
3) I placed a "Post" button so the visitor doesn't get confused with what "Add a Discussion" means. Note: you can not change the "Add a Discussion" in your Language Editor without changing it site wide. (that's why the "Post" button) Here's what I have it look like: (notice lots of keywords for this page)
A classified section targeted directly to surfers. Sell your new or used surfboard or surf gear here at no charge.
Post your Classified Here: (via "Add a Discussion")You can place this into your "Description" box. If you didn't already know, you can place html into the "Description" box of any of your Groups. BUT... you are limited to so many words in there so you'll have to play around with it. (I've been asking Ning to increase this for us but never a reply).
4) Using the Forum Discussions: This is where you can use the power of your Group section because each Group has its OWN forum. (This is why I have the "Discussion Forum" box unchecked BUT you still have it.) Create a Forum Topic for each type of classified category you think applies to your site.
5) Using the Comment box: Now you can place a category list with links to all your different Forum topics that you created. Each different Forum Topic being the name of each of your different Categories. I did my category list using a drop down menu from Jens site. When finished you just paste the html into the "Comment" box... I also placed a search box in there too...
6) Be sure to uncheck the "Comments" & "Discussion Forum" box under the "Features" via "Edit Discussion" under your Options tab when completed.
To see how I completed mine you can view it at: Classifieds for Surfers
Oh... and please feel free to critique my Classifieds