1. With that little RAM, you're going to hit swap hard & often. Find out how much RAM your mobo supports, and the highest speed it supports. If you can find that RAM type cheaply (used), max up, then disable your swapfile in system properties - advanced - performance - settings - advanced - virtual memory - change - no paging file. Don't ever overspend on old RAM types, since it normally makes more economic sense to go for a whole new mobo, CPU, and RAM in such cases.
2. If you can't do this, but you have more than one hard drive, set your swapfile up on its own partition on a hard drive other than the one you use for Windows and applications, preferably the first partition on a fast drive that is master on a separate IDE channel, where the drive isn't used heavily for much else. To use a custom swapfile with a static size, enter the same size for the initial and maximum size in the same virtual memory settings location quoted above. Swapfile must exceed the highest peak commit charge you think you'll ever see in task manager, and the partition size should be just enough to fit that swapfile. Then just never use that small partition for anything else. If you multi-boot different Windows versions, you can configure them all to use that file as swap to save on space that would be wasted on multiple swapfiles with different names and in different locations. If the file ever gets deleted somehow, the next Windows version to boot will recreate it in place, and it will not be fragmented because you don't have anything else stored on the partition. (My swap partition is formatted as FAT32 so that W98SE can use that swapfile as well, and also because FAT32 is faster than NTFS.)
3. If you can't even do that (maybe you only have one drive), download and run the following program at least once:
http://www.microsoft.com/technet/sysinternals/utilities/PageDefrag.mspx
4. In case doing everything in
>>2 doesn't already do this, turn off system restore and automatic updates in system properties (assuming you are running XP).
5. Turn off indexing service in Search for File or Folders preferences.
6. Uninstall and never use any live anti-virus or anti-spyware program that stays resident in memory. One-time inoculations like Spybot S&D's immunization feature are okay in case something tries to exploit IE. Instead of live anti-virus, just don't install random shit. You can run periodic anti-virus scans just to be safe, but never realtime scaanning if you want to maintain good performance.
7. If you want to keep using Firefox, go to the URL about:config by using the location bar. On that page, double-click on network.http.pipelining to switch its value from false to true.
8. In Firefox, if you want to keep Flash installed, consider using the Flashblock extension. That way Flash won't auto-run whenever a stupid site insists on loading some unnecessary shit (like Flash ads), and you can turn it on or off by customizing the toolbar and adding its toolbar button. For the same reason, disable Java and only enable it when you come across a site that really needs it. Doing both of these will heavily cut down on RAM and CPU usage when you have a lot of tabs and windows open.
9. Uninstall all unnecessary browser extensions and plugins.
10. Don't ever install the WMP plugin for Firefox or Opera.
11. For video, use Media Player Classic (mplayerc) or Windows Media Player 6.4 (mplayer2) instead of Windows Media Player 7.0 or higher (wmplayer).
12. Dump Winamp and use Foobar for audio. If you need to use a favorite Winamp inpuut plugin that doesn't have a Foobar equivalent yet, use the Winamp input plugin wrapper (sorry, forgot its actual name, and I don't have Foobar on this machine to check).
13. If you MUST use Winamp instead of Foobar, don't use its transparency features.
14. Learn how to use task manager to modify process priorities safely and temporarily in the processes tab of task manager. Don't do this often. To be safe, don't modify more than one process's priority at a time, and never by more than one priority level. And don't screw with system-related processes unless you know what you're doing; just do this on applications you think are safe to mess with. Be smart about it. This can be useful to, say, lower the priority of a CPU-killing operation that has to run in the background so that video or music playback doesn't skip while you wait. Multi-processor and/or multi-core rocks so much because you don't find yourself wanting to do this nearly as much (if at all).