I'm a newbie,i had install three operating system --win2000 pro,
RH9.0,win2000 advance server.When the computer starting,
i only can see two choices--linux and windows .what should i do
if i want to see three choices?
how to edit lilo.conf or else file?

OK I assume all three are on different partitions. Enter linux and make sure you know which partition each operating system is on. If you don't, type "fdisk /dev/hda" (as root). Press "p" to see your partition table. Write down all the relevant paritions (eg linux is on /dev/hda1, win2000 is on /dev/hda2 etc). If you have more than one disk repeat the above step for each one (eg "fdisk /dev/hdb", "fdisk /dev/hdc" etc). That is for IDE disks. SCSI disks are called /dev/sda, /dev/sdb etc. Make a copy of your existing /etc/lilo.conf file (call it something like lilo.conf.old). Edit your /etc/lilo.conf file (as root)and find the other=<whatever> section (usually at the bottom). Add a stanza for the missing parition:

other=/dev/hdax (/dev/hdax is the name of the missing parition that you gleaned from fdisk)
label="Win2000" (this can say whatever you like but it can't have spaces in it)

Save and exit. The type "lilo" (as root) at the command prompt. If it shows errors then you'll need to fix them up before rebooting. If all else fails restore your old lilo.conf and type "lilo". Then post your errors here. The successful output should look something like this:

added Linux*
added Win2000pro
added Win2000adv

The bit after "added" in every line should correspond to the "label=" line in your lilo.conf. The asterisk indicates which one is the default.

Open a terminal and type man lilo.conf . Read the manual, and this will answer all your questions...
If you still don't know how to edit lilo.conf , search for tutorials related with this subject in www.google.com/linux , you'll find many.
Regards.

In general -

Open a shell command line.

Type

su

press enter

Then type your Root password

press enter

then type

gedit /etc/lilo.conf

or use your favourite editor.

press enter

make the changes and save the file.