How do I interpret the Memory numbers in Windows Task Manager?

Here's an article that details the entire performance tab.

FTA:

Physical Memory (K)

The total physical memory, also called RAM, installed on your computer. Available represents the amount of free memory that is available for use. The System Cache shows the current physical memory used to map pages of open files.

Kernel Memory (K)

Memory used by the operating system kernel and device drivers. Paged is memory that can be copied to the paging file, thereby freeing the physical memory. The physical memory can then be used by the operating system. Nonpaged is memory that remains resident in physical memory and will not be copied out to the paging file.

Some enlightening but highly-technical articles:

Understanding Memory Usage in Windows 2000

Paged and Non-paged Pool Issues on Exchange 2000/2003

Pushing the Limits of Windows: Paged and Nonpaged Pool You need quite some time to read and understand Mark Russinovich's blog posts but it's definitely worth it.