A Quick question

Well, I am in computer club at school, and we got a person who asked us to fix his computer. His main problem is that the computer is really slow, and has many viruses. I just want imput on what to do, I know that we should run antivirus/spyware programs. I am currently running Avast, Spybot Search&Destroy, and Adaware SE 2007 to get rid of the viruses/spyware, and will probably run CCleaner to rid some crud he has on it. Basically, i just want to know if this is a good procedure, or if I am missing something. Easy question, I just dont wanna look bad on our first request.
Thanks in advance.