Ah Old computers....one thing that's good about PC's is that they are easily upgradable. You say you are not tech-savvy, so I'll attempt to talk to a "layperson" here...
1: Upgrade your RAM. This should be the first thing you do. I doubt your computer has 200 MB of RAM, as RAM sticks come in 128/256/512/1012/2024 increments. One way to tell how much RAM you have is to open up "My Computer" (usually not defaulted on the desktop for WinXP, but it can be accessed from the default start menu), and select "Properties". It should tell you how much RAM you have. I'm not advocating you maximize your RAM all the way up to 2 GB, 1 GB should be just fine for most home users.
2: I'm not sure what you do to periodically maintain your computer, but you should definitely do the following:
*Virus Scans (you should ALWAYS have an Anti-Virus program, I
recommend AVG anti-virus free edition, should be good for home
*Spyware Scans (Without getting into the tech-geek flame war over
it, Windows Defender should be good for home users as well)
*Disk Defragmenter (this is a biggie! Your hard drive is broken up
into segments, and Windows stores information in "chunks" of data
at a time, and when a chunk is bigger than the amount of space
left in the segment, it will store it on another portion of you
hard drive, sometimes "fragmenting" your files all over your hard
drive. This isn't necessarily a problem per se, yet it really
slows down your computer when it has to check all over the hard
drive when accessing a file, Under "My Computer", right click on
one of your hard drives, and select "Defragment now" under Tools.
If you can't find it there, look under:
Start Menu > Accesories > System Tools > Disk Defragmentor
3: Windows Registry.... Now this is more for advanced users. If you mess up your registry, you run the risk of Windows not even booting at all! I would recommend a reformat of your hard drive and re-install of Windows XP before I recommend tweaking your registry unless you are absolutely sure of what you are doing (even if you use those "registry cleaner" programs).
4: Cleanup of Windows Startup menu. Previously I mentioned Windows Defender, it has the ability to really adjust the programs that load when Windows boots up. I recommend using this only if you are absolutely sure of what you are doing. Most of the programs that load with windows are fluff and not needed (do you REALLY need Windows Live Messenger to load when your computer starts?), but even still, be careful when adjusting the startup list.
5: Cleanup of old programs you no longer use. Under Start Menu > Control Panel, open up the "Add/Remove Programs" Dialog. Check for programs that you never used or think you will no longer need. Do you really need that "AOL Preload" that came with your computer even though your ISP is something different...? Please be careful when removing programs though, you still want to be able to function normally! (You never know when you remove something it could come back to haunt you when you try to load that favorite game, or when you're trying to tweak that picture you uploaded from your camera only to find a "missing .dll" or "Windows needs to look for a program to open this file".
I am not a "Computer Scientist", a genius when it comes to computers, nor an IT geek. This has come from 2 decades of playing with computers, tweaking and adjusting, my own as well as my friends (I was the "computer guy" back in college..heh, my major was mechanical engineering). Please take my advice with a grain of salt, that being said, I hope I've helped you.