Simple solution for external memory writes on CycloneIII sterter board.

There a bunch of examples that use NIOS and DDR included in the startkit CD.

This topic has some usefull information about setting up the DDR controller for that board in this thread:

http://www.alteraforum.com/forum/showthread.php?t=2379

You can use lpm_ram_dp, but it's implemented in the FPGA's memory blocks. The starter kit has an EP3C25, so you'll have less than 600 kbit of memory available.