A properly maintained computer will provide you with substantially higher speeds, both via RAM and on the internet, regardless of your hardware setup and configurations. The second law of thermodynamics states that all systems atrophy (degrade) over time - well, here are a few tips on how delay the inevitable.
1Clean out all the junk left behind by browsers. To do this, you can use the Disk Cleanup utility included on the Windows systems, or download a freeware program such as CCleaner to do it for you. In Linux you can use Kleansweep or Bleachbit. Cookies and cache left behind by browsers can amount up to gigabytes of wasted space, so it is imperative they're deleted.
Search and destroy spyware and/or viruses on your PC. There is a myriad of tools available to do this. AVG Anti Virus is a good one to use. Download.com is a great place to legally obtain these tools.
Defragment your hard drive monthly to keep your computer running smoothly. Windows XP includes a utility to do this, but a tool called Magical Defrag also exists, which automatically defrags your system during periods of inactivity.
Uninstall programs you no longer use, and delete music you no longer listen to. The more free space your computer has, the faster it will go. You'll be surprised how much space you'll free up and how much your computer's performance will increase.