The first command I run on any new PC is FDISK... :)
While uninstalling software or preventing some "TSRs" from running on startup will make an improvement, most software installs a bunch of stuff that, once installed, can't easily be deleted. Though an Uninstall routine will do the best job, most are written to leave certain things behind, and some are just so poorly written that lots of junk is left scattered around your drive.
In addition, you may have a driver installed for a piece of hardware that is buggy and needs to be updated. Video cards are the biggest offender, with sound cards the next common.
Last, I'm pretty sure the Conexant modem is of the "WinModem" variety. In order to save money, they omit a controller chip (UART) from the modem and instead install drivers that use the CPU to perform that functionality. That means that whenever your modem is being used, your CPU is having a bunch of processing cycles eaten up just running the modem. By replacing the modem with a nonWinModem, you might see a decent improvement.
Oh, and DUMP AOL. Not only should you not be supporting this anti-rights company, but the AOL client is a resource hog, and has been known to spy on your files.
If all else fails, you can format the drive and reinstall Windows. You'd be amazed at how fast your PC will be. You'll also notice that as you reinstall additional software, you'll see the speed drop. Certain applications will be very noticable (for example, I hate the RealPlayer app, which takes forever to start and bogs things down). Anything that isn't vital to performing a specific task should be avoided; especially screen savers and the like.
Good luck!
-Troy