you need to make a partition to install Win2000 on.
Win2000 will set up a boot menu for Win2k/98 easily, and then from there it's fairly easy to add linux to the Win2000 boot menu.
Just boot to linux (probably using a floppy) and type
dd if=/dev/hdb1 of=/mnt/DOS_hda1/bootsect.lnx bs=512 count=1
(/dev/hdb1 has to be changed to the name of the partition linux's boot loader is on, and /mnt/DOS_hda1/ has to be changed to wherever your windows "c" drive is mapped on linux)
then add
c:\bootsect.lnx="Linux" to the end of the boot.ini in your c:
If you are using lilo now you will probably have to edit /etc/lilo.conf and make it so that it's not using hda's master boot record for itself because Win2000's boot record will want to be in charge.
But that's easy just change the first line of that file from hda to hdb1 or wherever linux is installed.
Edit:
Hmm ok well I don't know the specifics on the boot loader you are using...but the Win2k install will set up 98/2k for you, and the dd if= of= part is still fine, you just have to figure out how to move your bootloader off the MBR on hda
Edit 2:
here is an excellent partitioning/tri OS setup piece. I used the info in here the first time I set up Linux/98/2k...I was doing a fresh install of all 3...but you can still pick it apart for details 98 should come before 2000, and it doesn't make any difference when linux comes because you have to set it manually, so you can still follow it more or less.