If formatted as NTFS then Fdisk will not recognise he partion.
The bootcfg command is a Microsoft Windows XP Recovery Console command that manipulates the Boot.ini file. This command has a function that can scan your hard disks for Microsoft Windows NT, Microsoft Windows 2000, and Windows XP installations, and then add them to an existing Boot.ini file or rebuild a new Boot.ini file, if one does not exist. The bootcfg command enables additional Boot.ini file parameters to be added to existing or new entries.
To use the bootcfg command, start the Recovery Console with the Windows XP CD-ROM, and then click Recovery Console. Or, install the Recovery Console locally, and then select the command from the Boot menu.
it should be set active automatically if you have installed xp correctly. Is the drive being seen by autodetect? (check in bios settings or on post screen). If you want to check you can still use a startup floppy if you used Fat32 file system. If you used NTFS boot from the CD again to check.