I'm working with AVR Studio 4, in C,
and having a hard time finding info on how to access external memory...

 

What kind of external memory? It is also mostly a hardware problem.

 

Well, let's say I want to work with external flash memory.

 

An easy way would be to get an I2C or SPI flash memory IC. Using a serial
IC would use a minimal number of lines.

Check out the Microchip parts.

(* jcl *)