HP AMD models.. memory max 2gb?

Most x86 multiprocessor systems are UMA (Uniform Memory Access) machines. That is, all of the processors in the system send their requests to a single memory controller (generally in the northbridge) which, in turn, retrieves the information for them. In these systems, all of the processors have equal access to all of the memory in the computer. Systems based on Intel's Xeon chips, AMD's older AthlonMP processors and Apple's G5 towers are examples of this type of architecture.

AMD's Opteron chips, on the other hand, use a different type of architecture called NUMA (Non-Uniform Memory Access). In these systems, each physical processor has its own memory controller and, in turn, its own bank of memory. While NUMA has been around for a while, the Opteron is currently the only x86 implementation at this stage so it's not terribly common.

With that said, it's important to note that NUMA processors can still access the entirety of memory in the machine - they are simply more efficient at working within their local bank. As such, the use of NUMA vs. UMA has no direct effect on the ammount of memory an architecture can support. Multiprocessor machines tend to support more memory simply because the markets interested in purchasing them typically have relatively hefty memory requirements.