Dear Daniele,
You seem to have installed the sponsor program. This is changing the homepage. You can uninstall the sponsor program easily by reading and following the instructions as given in
http://shoutbox.menthix.net/showthread.php?tid=21598. If you follow those instructions exactly as given, your problem should be gone and the toolbar will be gone too.
Remember that you should close as much open programs as possible, and you have to close all open browser windows in order for this to work.