It might just be because its an AMD 2.3 GHZ single core trying to run Windows 7. That is more XP speed.
You could try reinstalling Windows 7 and slow rolling the install of other stuff.
Either that or just start uninstalling things one after another till the processor usage quits hanging out at 100%. Whatever you uninstalled last would obviously be the thing you don't want to reinstall as you put the other stuff back on.
What anti-virus are you using?
It could also be that between your OS and your anti-virus constantly scanning in the background that you have no resources left for other stuff.
Back in like 2000 when I was a network admin in a 2500 user environment with mostly single core desktops people used to complain all the time that windows + anti virus + office apps alone killed all their performance.
In the last few years I haven't seen that as much, because most enterprise desktops and laptops are multi-core these days so the OS and Anti-Virus can be handled by 1 core and leave 1 whole core for productivity apps, giving pretty good performance in general.
If the anti-virus you are using is something heavy weight (Symantec/McAfee) you might try something light weight instead like Microsoft Security Essentials.