A good start would be to install Win NT right now... because then you have the windows OS's working correctly and after that, on reboot you will get the NT boot loader where you can choose between NT and Win'98.
If all that works fine, flip in the RedHat CD and start installing RH.... just follow the instructions and let RH install LILO on the MBR (master boot record of your primary harddisk) which is the default b.t.w.
After install you will get LILO as a boot loader and you can boot Linux, to get NT and Win'98 to boot again you have tou reconfigure LILO:
login as root or su to root
add the following lines:
now safe the file and run lilo (you have to put the configuration file in the MBR by typing lilo at the prompt and pressing enter)
NOTE: /dev/hda1 schould ofcourse be your primary harddisk where Win'98 was installed and where NT left its ntldr, boot.ini, io.sys and msdos.sys files. in the case of an IDE disk this usually is /dev/hda1
after rebooting you can now type "windows" at the LILO: prompt to switch to the NT boot loader and there you an choose NT or Win'98 like you did before.