Create a partition for your win98/ME, be sure to leave some space for RH6... then install windows as usual... 
After your windows install, create the RH6 setup bootdisk, and boot up your PC with that... next, just go through the RH installation program, and create a Linux partition for RH during the process... When it's time to setup LILO, it should recognizes your windows partition and give you an option to boot into that... 
That's it... LILO makes it quite easy to create this dual-boot... remember to create the Linux parition in the space you have left for your harddrive... it is also a good idea to create a small third partition for linux swap too....