depends...r u running win2k on ntfs partition on the c drive? if yes, then a boot manager is needed.  If the file system is fat32, just install win98 using the "setup /ntldr" switch.  or install win98 as usual and then use the win2k cd to repair the boot partition of win2k.
no sure if u can use pqmagic to convert the ntfs partition back to fat32 without hosing win2k...if u can, then u can do the above as well...
if u r running scsi with 2 separate drives, u can disconnect the win2k drive...boot to the second scsi drive and install win98 there.  when u r done u will have two drives with active partitions.  to choose which drive to boot from, go to scsi bios and select the proper scsi id.