sure,you can.
just click on the
(customize this page) link on your "Main" page.
then u can see some options.like this:
Drag a "custom html" menu to your sidebar.
then it becomes a menu on your sidebar.click on the settings buton,like this
and click on it.a new window will open.write your html code in it,and save it.after that click in the "finish customizing" button as seen above.
You are done.
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oxwall has a separate advetisement plug-in.you can use this.visit:
This