This is my suggested method for installing Win98SE:
You will need a 98SE CD and a valid product key as Kruncher
said. You will also need a startup floppy - Go to Control Panel, Add/Remove programs and there is a tab for 'startup disk'. If you can't do that make one on another Win98 or Win98SE computer, they're not specific. You will also need drivers for the motherboard and any other hardware devices in the system - the essential ones would have come on a CD belonging to the motherboard. Is there someone to ask at work about this? If the drivers are not available then you need to identify the main hardware items mobo, graphics card, sound card, LAN card etc. and hunt these down on the internet. The motherboard chipset ones are the most important, Win 98 will load drivers for basic functions for the rest and you can update the drivers later.
Then these are the steps I would recommend:
1. Boot from the startup floppy with CDROM support and at the A: prompt type "FORMAT C:" without the quotes. If you are sure answer "Y" to the warning.
2. Put the Win98 CD in the CDROM drive. Because of the way the startup disk boots this will most likely be your E: drive.
3. At the A: prompt type "C:" (no quotes) return, then "MKDIR WIN98" return. This should make a new directory on your hard drive called WIN98. Check this by typing "DIR".
4. At the C: prompt type "E:" then "DIR", you should see several directories listed including one called WIN98. If not you are on the wrong drive and you need to try different drive letters until you find your CDROM. When you see WIN98 type "CD WIN98" then "COPY *.* C:\WIN98". This will copy the contents of the Windows folder to your hard drive (which makes installation and future changes easier).
5. When the copy is done type "C:\" then "CD WIN98". Do a DIR to check there are files ending in CAB present. then type "Setup".
6. Now you are in the Windows 98 installation program and you follow the prompts.
7. When Win98 has finished install the motherboard/chipset drivers and the drivers for any onboard devices from the mobo CD.
8. Now install drivers for any additional cards or peripherals from their manufacturers CDs.
9. Install Anti-virus software, anti-spyware software and a firewall. Then you can setup your internet connection. See the Tutorial here
before you connect.
10. Install your applications, reboot and your done.