1) To prepare a USB drive and install windows from it: I recently did this for a notepad without an optical drive, you'll need:  1.1) USB drive of at least 2GB, make sure is a real USB drive not one of those microSD USB adapters, some USB drives won't be able to boot,   1.2) download WinToFlash, is a free application that will format your USB drive and make it bootable.   1.3) The Win98 cd or iso image file, if I recall correctly WinToFlash asks you for the windows setup and copies the setup files into the USB drive.  1.4) Enter your BIOS and make sure the boot order is set to booting from the USB drive first  1.5) Plug the USB drive and boot your machine, it should go through a normal Windows 98 setup.  2) Installing Win98 on a different partition: during the win98 setup they ask you where you want to install the OS, you just have to select the correct partition, there is no need to boot from it, you have to boot from the USB drive.  3) About switching OS after you're done: you just have to make sure to switch back the boot order on the BIOS and have the hard drive as first option, at BIOS level it doesn't allow you to choose logical partitions just the drives, when the machine actually starts booting (after passing the BIOS screen) it gets to a point where it asks you on which OS you want to boot if you have more than one, if you don't see a screen like that press F8 while booting and it should come up.  4) About emulating win98 instead: I'm not 100% sure on this one but the times I've tried emulating old OSs in order to play old games it haven't worked quite properly, I remember trying to emulate win98 on a vista machine to play Dungeon Keeper and it did run but was unplayable, haven't tried a virtual machine like suggested, but I suspect it will end up being an emulation and not quite work anyway, I think having a double partition with a real old OS installed is the actual way to go to play old games. DOSBox is a DOS emulator and it has worked for me in the past at least for XCOM.