Amid the hoopla surrounding the release of Windows 7, Apple introduced refreshed lines of iMac computers. We took a look at the 21-1/2 inch model ($1,200 to $1,500) and the 27 inch one ($1,700 to $2,000). (See how we rated previous iMac models in our desktop computer Ratings, available to subscribers.)

Both iMacs have larger displays than their predecessors (20-inch and 24-inch respectively) and come with the latest Mac OS 10.6 Snow Leopard operating system. They include a newly-designed wireless “Magic Mouse,” and a wireless keyboard, both of which use a Bluetooth connection. (For a glossary of standard computer features, see our free Computer Buying Guide.)

Magic Mouse. This has a touch-sensitive top surface that senses left and right clicks and lets you slide your finger around to scroll a window’s content in any direction. Slide your finger up and down for a normal scroll, or with the “control” key depressed to zoom the whole screen for a closer look. It takes a bit of practice and some independent finger dexterity to use the scrolling, but we were able to get pretty good at it.

The mouse also lets you use a two-finger swipe to navigate back and forth in the Safari web browser, and browse album covers in iTunes and photos in iPhoto. But we couldn’t get that feature to work on either of our iMacs. Apple’s helpline wasn’t able to help us—the products are apparently too new. But we found an Oct 27th software update for the Magic Mouse on Apple’s “support downloads” website that fixed the problem when installed.

One aspect of using this mouse that could take some effort to become comfortable with is that your palm rests on the desk surface, not the mouse. You grip the mouse with your thumb and ring finger, leaving your index and middle finger free to click or swipe. And you have to lift your left-click finger before you can right-click. Some staffers found it tricky to learn, and one commented “If you didn’t like Apple’s Mighty Mouse, you probably won’t like this one, either.”

The new keyboard. It’s the same size and has the same layout as the one on Apple’s laptops, so it’s smaller than you may be used to. There’s no number pad. The typing keys are full-size, but the cursor keys are small. The Bluetooth connection was robust in our lab, even with several other Bluetooth and Wi-Fi devices working nearby: We were able to walk at least 50 feet from the computer and maintain control with both keyboard and mouse.

The displays on these iMacs are gorgeous. Colors rendered by the LED backlighting are deep and true, though only slightly more so than on the previous iMac. The 21½-inch is brighter than the previous 24-inch model. The 27-inch is even brighter: At its maximum setting, it’s a vivid 400 nits—brighter than any other computer display we’ve tested. And its LED backlight comes up to full brightness instantly, and has longer expected service life than the usual CCFL backlights. The display has a very wide viewing angle, both horizontally and vertically, making it good for collaborating with others on graphic design and gaming.

Design considerations. The new iMacs follow the trend towards edge-to-edge glass, losing the remaining thin aluminum frame at the top and sides. The entire back is aluminum, save for the Apple logo. The height of the area below the screen has been reduced, so the 27-inch is no taller than the 24-inch was. And the aluminum baseplate gets thinner towards the front, making the iMac seem to float above the desk. The keyboard can be stored almost out of sight atop the baseplate.

Apple had added a memory-card slot to the iMacs, the first ever in a Mac desktop. It takes SD and MMC cards. The Mini-DisplayPort on the 27-inch model can feed another monitor or accept digital video from a Mini-DisplayPort-equipped source, though you’ll need to buy a $30 cable to connect it.

Otherwise, the configuration of the new models is a step up from that of the old ones, with 3GHz Core-2 Duo processors (up from 2.8GHz), or a Quad Core i5 in the costlier version of the 27-inch. There is 4GB of memory, doubling that in the prior models, and four memory slots for expansion. Huge 1TB drives are in all but the cheapest model. All this adds up to slightly better performance in a line of computers that had top-notch performance already.

Coming up next: Our look at the new MacBook and Mac Mini. —Dean Gallea