Best option is probably to install DosBox and I’d recommend installing D-Fend with it. DosBox is a DOS emulator that plays nearly all DOS games extremely well, including KQ5. D-Fend is a ‘front-end’ for DosBox that basically makes configuring and loading games a lot easier, since it does all of the command line stuff for you that DosBox wants to properly load a game. If you install both and load up D-Fend, it’s pretty hard to set it up wrong.
Set the cycles to around 10000, it all depends on how fast your computer is. If you hit CTRL + ALT + DEL and click the Performance tab in Task Manager while DosBox is emulating a game, you can see how much CPU usage the emulator is using, basically you don’t want it at 100% because then the emulator will start slowing down. Then you just lower the CPU cycles a little in the emulator and adjust it until it’s playing good, but 10000 should be good if you have a decent computer.
Other than that, the only thing you need to worry about is ‘mounting’ the disks. When you’re creating a profile for a game, D-Fend will ask you to select which disks you want to mount. Easiest way is to hit Auto-mount and it will automatically configure C:, and that’s all you need to do unless it’s a CD game like KQ5 CD-ROM version, in which case in addition to mounting C:, you’ll also have to mount your CD drive (D: or E: usually).
That should be all. It might sound confusing reading, but if you try it out, it’s pretty easy. And then if you want, you can mess around with more advanced settings, like opengl or ddraw rendering (use opengl if you have Nvidia graphics, and ddraw if you have ATI). You can also try a different scaler. I like advinterp2x the best. It smooths the jagged edges.
There’s lots of other stuff you can do, but if you just want to play the games how you remember them then all you need to worry about is the drive mounting and CPU cycles. Unless you’re hoping to play with MT-32 sound, then you’ll have to figure out some other stuff.
You can also try VDMSound, which emulates Soundblaster cards rather than the entire DOS operating system. It works good for old games too.
If you want to play old Windows games, that’s harder to get working right. Best way is to make a shortcut of the .exe for the game, right click the shortcut and choose Properties. Click the Compatibility tab and select Windows 95, and select the other options there for best compatibility.