I need to assign new classes to certain areas coz i feel the skinning has had corners cut off, like in the control panel. Anyone tell me how to insert em?

http://www.w3schools.com

Look for the CSS tutorial on that web site, and prepare to hate the Easy CSS editor.

can't i change the class it assign on post view and add it to css?

Yah, but you will change classses all throughout the design.

no i mean on topic view i can change the current one and replace with a new one and add the new css to file?

yes, you can.

Or, you could just replace the CSS for the current class if that is possible for what you're trying to accomplish.