Undaunted by a copyright infringement lawsuit, Mac cloner Psystar has joined the ranks of e-retailers like Amazon.com and Overstock by holding a Cyber Monday sale.

The company, which sells low-cost knockoffs of Apple's pricey Macs, is offering free CPU, memory, and hard drive upgrades on a number of its models. It's also slashing prices. As of Monday morning, Psystar.com was pitching a fully configured Mac clone, featuring the OS X "Leopard" operating system pre-installed and a dual-core CPU, for just $554.

Psystar's Web site notes that the offers are good only on Dec. 1, which in recent years has come to be known as Cyber Monday as individuals returning to work from the Thanksgiving holiday use office computers to shop online.

Apple sued Psystar for copyright violation in July, alleging that Psystar's Mac clones infringe its copyrights. A judge last month rejected Psystar's claim, filed in a countersuit, that the Mac OS represents a discrete computer market unfairly dominated by Steve Jobs' company.

Psystar's countersuit claimed that Apple's control over the market for its own products violates Sherman antitrust rules and other U.S. laws. A Psystar victory could have paved the way for other PC makers, including big vendors like Dell, Hewlett-Packard, and Lenovo, to enter the Mac OS market and offer alternatives to Microsoft Windows PCs.

Psystar isn't depending completely on the Mac OS market. The system integrator recently introduced a Linux-based personal computer that sells for just $299.

Psystar's OpenLite system ships with the Ubuntu Linux desktop pre-installed, running on a 1.8-GHz Intel Celeron chip with integrated graphics support.

Upgrading to a dual-core Pentium chip costs an additional $40.