Here's my suggestions...
1. BACKUP YOUR IMPORTANT STUFF. I don't know how many times people ignore this. CD media is cheap, burners are cheap, USB Flash drives are cheap - make a backup strategy and STICK TO IT. Having 300GB of music, graphics, fonts, porn, whatever means nothing when (not if, but when) that 300GB drive dies. And last I checked, it was at least $500 for a professional data recovery place to just LOOK at a dead drive.
2. If you have 256Mb RAM or less, get more RAM. This goes double for those using a computer with on-board video, because that on-board video card can be using up to 128Mb of your 256Mb RAM for itself, leaving XP with just 128Mb of RAM to use. I'd recommend nothing less than 512Mb of RAM, 768Mb if you use on-board video.
3. If you have a free AGP or PCI-X slot, and use on-board video now, get a video card. Not only will it free up the RAM the on-board video steals from you, it'll likely run faster and perform better.
4. Use Add/Remove to uninstall anything you don't use. If you don't know what it is, chances are good you don't use it. If you aren't exactly sure, Google it or ask someone.
5. Decide what anti-virus and spyware tools you are going to use. Many folks decided that downloading every free anti-spyware/malware program and installing them is a good idea - it's not. Just like any other software, they sit there and hog up resources. I use and recommend AVG AntiVirus FREE Edition http://free.grisoft.com/doc/1
and Microsoft AntiSpywarehttp://www.microsoft.com/downloads/d...displaylang=en
. Both serve me well and have kept me protected. I find Norton AntiVirus to be bloated, slow, and a resource hog - and I abhor the idea of having to pay for automatic virus updates. Alternates to the MS AntiSpyware are Ad-Aware SE Personal Edition and SpyBot Search & Destroy - both available via download.com - and I give the nod to SpyBot based on personal experience and the fact that it can proactively protect your system from changes.
6. I recommend CCleaner http://www.ccleaner.com/
- it does a wonderful job of cleaning up broken or failed program installs, temp and cache files, and the like.
7. I also recommend HijackThis http://www.spywareinfo.com/~merijn/
. HJT scans your system and can produce a report. By posting that report, others can assist in identifying things that should be removed - like background processes and browser "helpers." You can also remove them using HJT - but it's also an unforgiving tool and gives you the capability to really screw things up, so be careful.
8. Running a P2P (peer-to-peer) file sharing software program is like opening the door and cheerfully inviting the scum of the earth into your PC to cause havoc. There are plenty of free file servers out there to use instead if you need to share a file with someone.
9. Browse both the web and your email SMARTLY. There are plenty of free email services with 2GB or more of storage - pick one to be the email you give out when signing up for things on the web. If it's something you will keep, you can always change the email that uses later. Of course, don't even open emails that you did not ask for, or from untrusted sources. Be careful when clicking on links or pop-ups from web pages. Or - especially - links from IM clients like AIM.
10. Beware of phishing scams - emails that claim to be from eBay, PayPal, a bank, etc - and that ask you to click on a link and submit private information. Hover on that link - and in the status bar at the bottom of the window (most email clients have one, you may need to enable it) it will show the REAL destination of the link. Right there you can tell if it's fake or not. Understand that eBay, PayPal, et al will not request your information in this way, but scumbags will.
I know that didn't just deal with system performance, but it's all good stuff