Dell Inspiron Mini 9 (click for larger image)

Dell on Thursday officially launched its long-awaited mini-notebook, jumping into the sub-$500 ultra-portable PC market where the computer maker will be battling Hewlett-Packard, Lenovo, Asustek Computer, and others.

Details of the Inspiron Mini 9 have been available for quite a while on the Web, making Dell's announcement anti-climactic. Price, however, remained an unknown until the official release.

The Windows XP model is available immediately in the United States, Canada, Japan, and select countries in Europe. Pricing in the U.S. starts at $399. The Ubuntu Linux version, expected to be available in a few weeks, will start at $349.

The Mini 9, which weighs 2.28 pounds, has an 8.9-inch LED display with a resolution of 1024 x 600 pixels and is available with built-in Wi-Fi and Bluetooth wireless support. A Webcam comes with the XP model, but costs extra on the Linux version. The system supports up to 1 GB of memory and is available with a 4-GB, 8-GB, or 16-GB solid-state drive. The mini-PC is powered by a 1.6-GHz Intel Atom processor.

With the Mini 9, Dell is including 2 GB of online storage from Box.net at no charge. The system is available in black or white, but the white case will cost extra.

Dell's latest offering tosses the computer maker into a market that's on track to reach shipments of 5.2 million units worldwide this year and 8 million units next year, according to market researcher Gartner. Manufacturers could ship as many as 50 million devices in 2012.

Mini-notebooks are defined as sub-$500 lightweight PCs with screen sizes 10 inches or less. While limited in functionality, their size, ease of use, and low cost are expected to attract buyers looking for an ultra-portable device for e-mail and Web surfing on the road.