Your installation of a single 4GB SODIMM module with good results encourages me to try, as well.
To ensure I match your procedure, what is the specification of your DDR2 memory module? That is, the “speed” (667 or 800 mhz) and memory timing (usually 5-5-5-15/18). You probably used PC-5300, but I wanted to be sure.
It also would help to have a link to the seller and/or phone, if available.
Many thanks for your posted message— I’ll reply with my results.