Prior to installing, enter BIOS ( Setup ) and make sure the CD/ROM the first boot device. Put your XP Disc in the drive and disconnect all external peripherals except the keyboard and mouse, and be sure those are not USB.
Once you set your BIOS to boot first from cd . . when it restarts you will see a black screen with a prompt "Press any key to boot from cd" . . do that and you will be able to delete partitions and recreate the ones you want and proceed to formating and installing XP
That message can pass quickly, so have a finger on the keyboard when you boot. This will delete all data on the drive so be sure you have your important data backed up.
This is a good guide to reinstalling XP . . you might want to print it for reference during the install.
http://www.winsupersite.com/showcase/windowsxp_sg_clean.asp
as is this:
http://www.doverproductions.com
You will have to reload drivers and applications, After the installation, you will need to download and install the MicroSoft Critical Updates. Alternately, this would be a good time to install SP-2, while windows is clean. Prior to connecting to the internet be sure you enable the XP firewall.
If you want to save your files and settings from the win98 installation, you can use the XP Files and Settings Transfer (FAST) wizard to create an image of them and save to cd or other removable media. This is a good guide to using the FAST wizard
http://www.winsupersite.com/showcase/windowsxp_sg_fstw.asp
Good luck and have fun . . wrs