It sounds like there are too many TSR programs running in the System Tray (the icons by the clock). You must turn off all the non-essential programs to free system resources (RealPlayer, CD notifications, AOL, etc.) Start these programs manually only when you need them, then shut them down.
Go to
\Start Menu\Programs\Accessories\System Tools\System Information\Tools (menu)\System Configuration Utility\Startup (tab)
to see what Windows loads when it starts up. I am sure you will find a lot. Turn off items which you do not need - leave hardware configurators (like WinModem stubs), the SystemTray, LoadPowerProfile, TaskMonitor, ScanRegistry. SchedulingAgent (if you need it), any video card TSRs, HIDSERV (if, and only if, you have a Human Device Interface object that you still want to work (like push buttons on USB speakers)) and anything else that looks necessary. Turn off everything else. Reboot and check your System Resources.
If you still are having problems one of your programs may have a memory leak. Watch for a pattern of memory loss then go to the program's website and look for a patch.
Your mileage may vary...