No you don't, you just need to make an ad-hoc build of the app, unless you need to install it on more than 100 devices (that's the most apple allows for ad-hoc).
You need to know the UDID (basically a long serial number) of the devices you're installing it on, then you create a 'provisioning profile' for the app. You sign the ad-hoc build of the app with that profile when you build it, then you deliver both the app and the profile to the people you want to install it. They just drag both files into iTunes and it'll install.
Apologies if that didn't make much sense, but an iOS developer will already know this and it'll make sense if you've built an app.