As far as I am aware and unlike Win2K or XP, Win98se does not have the automatic ability to dual boot.
You can overcome this, by loading a boot manager on C:. This will take over the boot function and give you a menu to choose which operating system you want to boot into.
Boot Magic, part of the popular Partition Magic suite is a good one, but if you don't have that, a simple search will throw up plenty of options.
click here for one option that can be loaded with Win 95. As a general rule, you install the oldest system first.