koala

You could probably remove a few programs from your msconfig startup list, or use the options in each program to prevent them from running at startup, like nerocheck, quicktime, webshots and itunes, but none of these are resource hogs that would slow down your system significantly.

Thayyibahmed's suggestion of CCleaner, along with regular defrags, will help keep things running smoothly. Just be careful which options you select in CCleaner or you might remove more than you wanted to.

Increasing the RAM is always a good idea with XP. 512MB is recommended as the minimum, and you'll see a big performance increase with 1GB. With only 448MB RAM, Windows is probably using the swap file alot of the time to make up for the lack of memory. This is located on the hard drive rather than the RAM chips, so is much slower. Go to Control Panel > System > Advanced tab > Performance Settings button > Advanced tab > Change button. Set the Custom Size to 2048 for Initial and Maximum, click the Set button, then OK out and reboot to complete. This will give you a large static swap file.

If you've never opened the case, now would be a good time to check the fans are all spinning and to blow out any dust with a can of compressed air. The build-up of dust and dirt around the fans, heatsink and card slots is a major contributor to heat problems and system slowdowns. Your temperatures look ok though. Take them again while running a 3D fullscreen game to stress your system (alt-tab back to SensorsView during the game, not after). Also note the PSU voltages, especially the +12V reading.

Please list all the security software you have installed. There might be a conflict between realtime monitors that run in the background.

Run some malware scans and post back with the results.

In what way does the computer feel slow? Is it the framerates in games, occasional mouse lag on the desktop, programs taking too long to open, constant hard drive activity, etc?

As a last resort, you could backup your data, then format and reinstall Windows. A clean install is a good way to get performance levels back to how they were, but only if the slowdown is not being caused by a hardware problem. We can help you through this procedure if nothing else works.