how to add a rotating banner to SMF 2.0 RC1 ?
You'll need to either insert ad code manually into the template or use the ad management mod.
Depending on the level of control you want, you might want to look at OpenX (http://www.openx.org/) for rotating the banners. You can add the code from openx into your templates.
I use the ad management mod under 1.1.8 and it is very easy to use!
Try searching:
Some might help, the process is very similar in 2.0 edits of logo/index.template.php files.
banner random rotation (http://www.simplemachines.org/community/index.php?topic=239828.0)
Changing Forum Logo each time it loads (http://www.simplemachines.org/community/index.php?topic=226078.0)
But you're a little vague with exactly what you want.