MBR=Master Boot Record.

Its that part on your Hard drive where all the critical information is stored...the partition table who is Primary and where they start, etc.

I am not very experienced with Dual Booting with Linux (I just started using RH8 like a week ago personaly). But I know for certain they dont play well, and that unless there is some cooperative multiboot function, you are going to need to stealth the Linux partition if you want 98 to be primary.