Can anybody help me how to add plugins. I have them downloaded, but they come up as a .sit file. What do I do?

http://www.stuffit.com/mac/expander/index.html will get the file open for you, there should be install instructions in the package or on the site.

Thank you so much.

Could you tell me a place were I can get the whole sliptscreen plugin for free without the writing of the company all over it?

Could you tell me a place were I can get the whole sliptscreen plugin for free without the writing of the company all over it?

Likely you have to buy it.