Help me get rid of this virus please.?

My computer has started to behave oddly. It's slowed down and my toolbar looks different. I think I have spyware or malware now. I downloaded Spyware Blaster but will it remove the threats? If not what can I do?. Is there anything I can do to clean my computer or do I need an expert? I also have Norton protection installed. I'd really appreciate some help to sort this. Many thanks.