When you first power on your system you should see something on the screen that says press this for setup. It should be DEL (delete key) or F1 F2 something like that.
Once in the bios see if there is a menu labled boot at the top, select this and make the CDROM following the onscreen directions the first bootable device.
If you do not have a menu called Boot then look under advanced you should find a section that has A,C toggle through the options until you get CDROM, A, C
Either way save changes and exit the BIOS.
With your Windows CD in the drive power up again and you should be prompted to install windows.
Now if you cannot boot to the CD then you will need a bootable Diskette with CDROM drivers : anyone running windows 98 can create one of these boot disks for you or you can download one online at
http://www.bootdisk.com
Once you boot with a 98 bootdisk just type in the drive letter of your CDROM which you should see asigned as the last part of the boot up.
Type setup and press enter. Follow the prompts. Hope that helps. Good luck