Do you have more than one partition on your hard drive? If not, I recommend that you create two partitions: one with the operating system and one with your data. It would reduce the chance of lost information. Or better yet, two hard drives.
BTW, I use Windows 98. I have been thinking of upgrading to Win2k, WinMe, or WinXP. Nice thing, I can actually install windows off of my second partition (don't want to have to whip out the install CD everytime I make a change).
I recommend that you also plan on making a few additions. Install a good firewall program. I use ZoneAlarm. Monitors network access. You can keep certain programs from accessing the internet while at the same time letting others through. It blocks ALL external attempts to access your computer.
Also, get a good Anti-virus. I use Norton Antivirus. I have mine set up to monitor EVERYTHING. I once opened a folder and it found a virus on one of the files. Also stops viruses from being downloaded.
I personally do not recommend leaving your computer unsupervised while a file is being downloaded. Allows you to stop problems before they get worse. If I need to download something huge, I set aside a day so that I can watch it.
To bad about your data. I hope you find some of this info useful. You probably know all of this already, but it bears repeating. The internet can be dangerous. If you keep to these recommendations you will be that much safer.
If you need anything, I have 1,892 ships one my computer. Some may be duplicated by accident but I will be happy to share.