Text Widget Issue on Themes

I'm brand new to WPMU & Buddypress. Prior to joining here, we installed both and have played around and spent alot of time finding and uploading themes. I am finding that several of the themes I have been testing - I am not able to insert html or other coding into the "Text Widget"... it is showing the actual html coding itself on the blog as opposed to the ad image/google ad. Is there some sort of setting/fix that needs to be done within WPMU to have the text widgets on these themes work correctly?

Thanks for any help.