Or simply check in your BIOS if you have the choice to choose which specific HDD you want to boot!
If so, find another HDD and install DOS 6.22, and all your DOS programs/games on it.
Since DOS 6.22 is FAT only, you'll see only the DOS partitions and have a nice standalone system.
On the other HDD, install Win98SE, with all your Windows stuff, and you can access the DOS partitions from Windows to tinker and stuff (if you want, you could even transfer files via USB in Windows to your DOS partitions.)
Now it's up to you from your BIOS to change which HDD you boot (either the DOS drive or the Win one.) And if you're ever tired of Windows, or build another PC, just yank the Windows drive out, and you have a nice native DOS system. It's also true the other way around.
Also consider that this way, each OS has its own drivers/hardware configurations. And if any of your drive fails, you still have a completely working system. 😀