I was messing around with an old copy of Windows 98 SE. I consider 98 SE for it's time to be possibly one of the most inovative OS's MS ever released. It was fast (though most computers that ran it now struggle at running modern software), it included loads of new features such as zip support (if MS Plus was installed), FAT32 support, easier updating, improved stability over 98 first edition, better USB support, and loads of under the hood fixes. Microsoft killed support for the OS back in 2006 (ME was also killed on that date, though 98 and 98 SE were supposed to loose support in 2004 or so, but it still had a huge user base). Never did they release a service pack for 98 SE. While toying with 98 SE I found that there is an Unofficial Service Pack for 98 SE. It is really a set of unofficial bug fixes and stuff that was unofficially back ported to 98 SE, along with tweeks and other neat stuff. This pack is pretty useful if you still use 98 SE (it is not for 98 first edition). Don't install the swap file enhancements unless you have 64 megs of ram or more. I also reccomend making sure you have all the updates MS released for 98 SE. This pack does the following:
Replaces notepad with a better editor
Apples many patches
Enhances USB support (I think it installs generic mass storage drivers)
Allows for you to optionally enhance your swap usage with tweeks
Can install a Windows 2000ish theme to the OS
Can change the shutdown and startup spash screens
A hand full of other things
There are a few other nifty little tools for those that still use 98 SE (and some work on other OS's as well). This page has several backported upgrades and patches for 98, 98 SE, and ME. This page has generic USB mass storage drivers for Windows 98 SE to let you use flash drives. There is also an unofficial daylight savings time fix for 98.
Of course before you do any of this, you should make certain you have all the latest updates from Windows update. Install all the security updates, especially IE 6.0 and all the patches. If you haven't done so, install Windows Media Player 9.0 and the latest DirectX MS offered to 98, as well as the latest .net. After installing, reboot and make sure there aren't any others (some fixes for WMP and DirectX and .net and IE appear after those are updated). Oh and this does take up a noteworthy amount of HDD space.
While 98 SE is still very much an old OS, as the old Monty Python saying goes "he's not quite dead".