This might help:
http://www.itforcharities.co.uk/donorinf.htm
Since the charity probably won't require your operating system, the easiest way to delete all of your data (including your OS and all of your programs) is to format the hard drive. (MI5
might be able to recover a small amount of data after a format but the type of people who search PC drives for personal data for criminal uses won't be able to do so).
Formatting your hard drive is really easy. You should already have a Windows 98 startup disk. (If not, put a floppy disk into the drive and go to Start > Settings > control Panel > Add/Remove Programs > Startup Disk > Create Disk. With the disk in the floppy drive, restart your PC. This should start your computer in DOS. Choose the option to start with CD support if you intend to reload Windows 98 (or any other OS) after reformatting. Otherwise, choose the final, 'minimal' option. Type 'C:format' (without the quote marks), hit 'Return' and your disk will be formatted.
The previous paragraph assumes that your PC is set to boot from a floppy ahead of the hard drive (which is what most Windows 98 PCs will do). If your PC doesn't boot into DOS, but starts Windows instead, you should try restarting while holding down F8. If that doesn't work, you'll need to enter the BIOS to change the order in which the PC seeks a boot source. (Try holding down the 'Delete' key while restarting).
If you've used the 'boot with CD support option', so that you can reinstall Windows, read the on-screen information to check which drive letter has been assigned to your CD drive. (It's usually E, not D as you might expect). After formatting, insert the OS disk into the CD drive and type 'E:setup' (without the quote marks) and hit 'Return'.
Chris