CPU usage. Usually 100% 2.4ghz p4. Is this right?

Ok, running Vista with 2.4ghz p4 and 1.7gb Ram. 512mb x1650pro agp graphics card. My computer is continually running at 100% cpu usage... This makes no sense to me.. In my task manager I have alot of services running that Im not sure what they are. My networking is at 0%, so im pretty sure its not spyware. I upgraded my system last week, added the ramm and the graphics card, along with a hard drive. Also, upgraded the power supply. What could be causing this??