If you’re looking for a cheap Mac notebook, don’t go to an Apple Store. You’ll be out of luck. However, some folks at Cult of Mac just published an article about how to use an eeePC or an MSI Wind with Mac OS X. It seems to work quite well, even if it is not totally legal.
OSX was installed on an ASUS eeePC 1000H, that has a 10-inch screen, a 1.6 GHz Intel Atom Processor, 1-GB RAM, and a 80 GB Hard Drive. According to the personn who performed the installation, the performance is quite good (similar to a MacBook or a G5).