The quickest and easiest way would be to download and extract a
Windows 98 bootdisk
Ensure that the boot order is set to Floppy Disk in BIOS
(press DEL on start up of your system, choose BIOS features or Advanced features option, )
Once the system is rebooted, choose the
Start without Cd rom support option
Type in
Format C: to format the Hard drive (I always hate telling people to do this, it normally signifies failure!!!)
Reboot the system again with the Windows 98 boot disk in the floppy drive and the Windows 2000 disk in the cd rom drive and choose
Start computer with cd rom support option
Type in e:\setup (where e: is the cd drive)
Install Windows 2000