You should look into the gog.com versions. They work on Windows XP, Vista and 7 in both 32 and 64-bit. In addition to the games working on almost all modern operating systems, they're also DRM free, which means once you pay for it, it's yours. You can re-download it again however many times you want on as many computers as you want. The only significant downside to the gog.com versions is that they come in bundles. You can't currently buy each game individually. KQ 1-3 are one bundle, 4-6 another, and 7 and 8 the final one. Each bundle is priced at $9.99.
To play King's Quest 5, I highly recommend you try out
ScummVM, a free and open-source program that replaces the installer files of many old games, including some of Sierra's finest (KQ5 included) and allows them to be played on virtually any device that supports scummvm. The glory of scummvm is that it's ported to almost all major devices known to man-kind, whether officially or not. I've been playing the enhanced version of KQ6 (which was only made for windows, not DOS) on my mac for some time using ScummVM. It works perfectly with no errors whatsoever for me. Try it out. All you'll have to do is point ScummVM to the location where your game is installed, and it will do the rest! There are instructions on the site on how to use it I believe. Someone actually played KQ6 on a PSP using ScummVM. It's also available for android, though I haven't gotten it yet; I'm not on Froyo, and I'm not sure if it supports Eclair (or, as some may know it, Android version 2.1).
