|Is the hard drive being detected when it reboots? If so, is it in the boot order in cmos/bios setup? There's no non-booting floppy disk in the floppy drive? Check to make sure the hard drive data cable is tightly connected on both ends and is in good condition.|
If the above is all correct try the setup again, but this time delete the existing partition and then recreate it. That'll be an option on one of the 'install windows' menus.
Besides that the only other thing would be the hard drive isn't set active. A hard drive must be set active in order to be bootable. Is there a second hard drive in the computer? Usually only one drive is allowed to be active so if another drive is already set then you can't set another one active without third-party software.
Setting it active should be done automatically when XP sets up the drive. I don't know how to check that using the XP cd. But you can set it active with a 98 floppy bootdisk. You just boot up with it and at the a:\> prompt type FDISK and enter. Y to large disk support and then from the menu it should tell you if it's not set active. You use option 2 to set it active. (You can download a file to make a bootdisk from a place like bootdisk.com.)
Then exit fdisk, remove the floppy disk and restart the computer, booting from the XP cd and do the installation.
You're not really green until you're soylent green.