Kohl, you did not give details about your CPU and RAM.
RAM (SDRAM or DDRAM?) allocates space or memory reservation for various softwares running at the same time, the more applications you run at the same time, the slower will be the response, dependent upon your memory capacity, sometimes it will give like a graphical presentation effect (like powerpoint slide presentation) before the next program or application maximizes its windows, sometimes the display freezes, sometimes it leaves white spots or white square or rectangular spots in the display.
These occurs when you are running a lot of applications in the background like an anti-virus program, spyware or adware programs and you have a low RAM capacity.
Before an application runs, say MS Office, the application is filtered first thru the anti-virus, and as you go along, the anti-virus software keeps working in the background.
Did you install Ad-aware and Spybot to be launched when windows start? Dis-able it, just run the application from the desktop when you need to, leave your anti-virus software's installation as is,you need to keep it working in the background always.
Try to scan your hard disk for bad sectors by running scandisk if you have it (the scandisk application can be created by making a start-up floppy disk), it is better than checkdisk, time consuming though.
Defragment your hard disk.
Try to lower screen resolution, update video card driver.