how to call a script every (say) 5 minutes

Hi all, can someone point me to a quickstart to the following problem? I'd like the OS to call a Script every (say) 5 minutes, that does some time comparisons (like: "hey, you ought to see your customer in one hour" or the like) on some database thingy. Basically i'm just interested in how to perform a script every given amount of time under Windows (2k, XP) and Linux. I don't know to much about cron jobs or the windows scripting host, but i thought something along the line might work out. thanks in advance Jan