If it's a older laptop, I'm not sure I'd suggest installing W98. How much RAM does it have and what size hardrive?
If you do decide to install W98, first your going to need a W98 boot diskette. And before you fdisk or format the drive, I'd suggest booting to the W98 boot diskette and checking to be sure you can access the CDRom drive. Insert the W98 boot diskette and power on the laptop. Assuming it boots from the floppy, select "Start With CDRom Support" from the boot menu.
Somewhere on the screen at the very end, it tells you what drive letter it has temporarily assigned to the CDRom drive. It will look something like this, "Drive X =MSCD001", where "X" is the drive letter that's been temporarily assigned to your CDRom drive for the install. At an a:\> prompt, insert your W98 CD and do this from the prompt to see if you can read the drive. Replace the letter X: in the command below with the letter you noted earlier.
dir X:
You should hear it access the CDRom drive and then it should display a directory list of the CD on the screen. If that occurs successfully then you will have access to the CdRom drive to install W98 from the CD. Do this to install W98 ......
fdisk
Leave the default set to "Y" for large disk support and press enter.
Now use the option to "Delete Partitions". Delete any and all you see listed. Now take the option to "Create a Partition" and create a "Primary DOS" partition. Take all of the defaults during the Primary DOS partition creation.
Now after the PC has restarted, key in the following and press enter.
format c: /s
When it's done insert your Windows CD. Then key in the following command at the prompt and be sure to change the drive letter, "X", to the drive letter that was temporarily assigned to your CDRom drive that you should have made note of earlier.
X:\setup