How can I play Police Quest I on Windows 7?
You're in luck.
GOG.com sells the entire Police Quest series for ten bucks on their website. This includes launchers that'll let you run the games in Windows 7.
I'd rather comment this but I can not comment yet, probably too low rep.
GOG.com sells it but here you can get the installers for free if you own the original version(s). Lots of sierra games made compatible even for X64 systems. May need some fiddling with some settings though.
http://www.sierrahelp.com/Patches-Updates/NewSierraInstallers.html#PQ