GWats,
Before the tutorial, lets begin with what you really want to do. Re-install is obvious, but you also need to format your hard drive. This means (essentially) erasing everything on the hard disk. When you re-install the OS, you should only see the OS and none of your previous files. It doesn't sound like this is what you did before, however you need to do this.
Secondly, what type of data are you trying to save? Will it fit on a floppy? CD-R? DVD-R? Do you have any of this equipment? If you don't have access to a type of removable media, this transition might be hectic. Are you worried about programs you have installed? If you have the installation CD's then re-installation should be cake. However, make sure to backup any files created from these programs after the initial install. E.g. MS word documents.
Throw away a 650? I wouldn’t. One of my computers is a 733mhz (not noticeably faster than yours) and it runs fine. However, I run Windows 2000 and I have 384mb of RAM. If you’re worried about speed surf the Internet for some RAM, which will improve your system’s performance drastically. (We can help you get RAM for your system if you want it) If you can, get yourself a copy of Win2k, it’s a HUGE improvement over Win98. You won’t believe the difference. Error handling, support, stability, and yes CTRL + ALT + Delete does work on Win2k. Believe me, I’ve dealt with Win98 for many years. (I feel your pain)
But, before any of that, please just give us an idea of what your options are in terms of backup, and what exactly you are thinking about saving. We'll move from there.
J_