There are definitely several free programs similiar in nature to print-screen. The problem with most of them is you're restricted to copying the whole screen, or, as Kermit mentioned, the whole active screen, then, as you just copy it to the clipboard, you must open some other program and paste it. With 'snip', you select any portion of what you see and that's all you need to snip. Then, if you right-click, you can save it anyplace you want. For example; if I'm browsing this, or another forum, or surfing the web and see an interesting post, picture, etc. I can 'snip' just a small part of a paragraph or the head a shoulders of a picture, save it to the desktop and review it later or file it in a more appropriate place.
Burntcav gave an excellent description on accessing 'Snip"; however there's a possibility that 'Snip' hasn't been activated in your particular computer. If that's the case, when you search for Snip or go to accessories you won't find it. Here's a few more details: "If you have a version of Vista other than Home Basic, you already have the Snipping Tool screen capture utility: Choose Start, All Programs, Accessories, Snipping Tool. If you don't see it there, it may not be activated. Go to Control Panel and open Program and Features (you may have to click Programs first). In the task pane on the left, click Turn Windows features on or off. If necessary, click Continue when prompted by User Account Control. Scroll through the list of features, check the box next to Tablet PC Optional Components, and click OK. Turning on these features gives you not only the Snipping Tool, but also the Tablet PC Input Panel, Windows Journal, and other stylus-related features.