What kind of processor and mobo? Is it on a LGA 775? This sounds like a pretty old build and maybe not worth upgrading unless you have access to cheap extra parts. You might want to do a full CPU/MOBO upgrade. Also, how much ram do you have? Not having enough memory can contribute to a slow computer. CPUz can give you a full report of your hardware btw.
Yeah I would look elsewhere to diagnose your performance issues. I have configured many even single core Pentium 4HT's @ 2.8-3.4Ghz with windows 7 and they run just fine. I would look at spyware/start up programs/ old files/ registry errors. Download CC Cleaner and malware bytes, run both and get back to me.