memory voltage question

My mobo specs say 1.8v for ram. I currently have 2.0v ram installed that I used in the previous mobo. I'm looking to get new ram and wondering do I have to order only 1.8 ram or is there some leeway and if so, how much?

The spec. of 4 x 1.8V DDR2 DIMM sockets means a power supply of VDD:1.8V±0.1V. If I'm correct the Memory voltage option in your BIOS starts at 1.90, w/ 2.0V also in white... while any voltages 2.1V and above appear in red.