There are many ways to make a computer faster such as more computer memory, a faster hard drive, a new cpu. If that does not work, then reinstall Windows or your Mac operating system. And to take it to the extreme to just buy a new faster computer. All these requires downtime and money for the new parts.
Being in Technology for 15 years, I can tell you that one of the best ROI (Return on Investment) method for its free to low cost and the minimal downtime is defragging your hard drive. As we use our computers by opening and closing programs, moving and saving files, or downloading music, the hard drive get fragmented and would take longer to run. The could be resolve by using a disk defragmenter program such as from Microsoft (free) or a 3rd party company such as from DisKeeper (recommend. About $40).
The Windows Disk Defragger that comes with Microsoft Windows does an ok job. It can be access by clicking Start -> All Programs -> Accessories -> System Tools -> Disk Defragmenter (See image1). The program would take a while to complete and even after rerunning it a few times in a row, I still find that my hard drive is not completely defragged.

I have been using the DisKeeper defragger for over 10 years and highly recommend it because I found that it is about 3 times faster than the Windows version and have more advance features. Also wanted to mentioned that I don't have any stake in the company even thought they offered me a job a few times. You could purchase the program from computer stores such as Office Depot, Staples, etc. or online.
Here is why I recommend DisKeeper and why I would say defragging your hard drive would be one of your best PC investment. Even after using the Windows Defragger, my hard drive looks like below. Blue is good, White means free space, and Red means Fragmented (Bad). Notice how much red I have on my partition. It is about 65% Fragmented! Anything over 8% would start to slow down your computer. My D Drive is actually about 98% Fragmented.

If I would get my hard drive defragmented, the improvements would be great. It would go down from about 300 to about 3 from the bar. Notice that this is minutes and not seconds. It is currently taking 42.7 times longer than what it should be based on the bottom right of the image.

There is no other way of improving your computer speed that tremendously and with such low cost that I know of. And by speeding up our computer, it would actually save us time as real estate professionals. I am planning to post something similar for the Mac and a few other ways to get more from your computer soon.