You've not stated what version of Windows the laptop has or what type of drives it's got. Basically you need to boot the laptop from a Startup disk, format the drive, then install Windows.
So first you need a startup disk. If the laptop has a floppy drive, that's probably the easiest way to make one (unless, of course, you've already got one). Put a blank floppy in the drive. Go to Add/Remove Programs. Click the Startup Disk tab and then 'Create Disk'.
Hopefully, your laptop is set to boot from a floppy ahead of the hard drive. Leave the boot floppy in the drive and restart the computer. With a bit of luck, you should see a screen asking you how you'd like to boot the laptop. Select 'minimal boot'. Wait until the prompt and then type
C:format
Hit 'Enter' and confirm that you definitely want to format the hard drive.
When it's finished, restart the laptop but this time select 'start with CD support'. Watch the screen to check which drive letter has been allocated to the CD drive. (It will probably be E, not D). Type
E:setup
Hit 'Enter'
Follow the prompts and Windows will install itself.
(Since your mouse driver won't be installed at this stage, selecting options is achieved by using the arrow keys and 'Enter')
If, when Windows has been installed, you find that there's no sound or you can't change the screen resolution, you might have to download and install the relevant drivers.
Going back to the step where you needed to boot from the floppy, if this doesn't happen (and Windows boots instead), you'll need to change the order that the laptop looks for boot devices. Restart the laptop and press the relevant key to enter the BIOS. (Usually Delete or F2). Then locate the boot order option and set it to use the floppy drive first.
If your laptop hasn't got a floppy drive, you can do the same thing using a boot disk on CD. Read the