Your Mainboard is D2348.
So this means you can have a max. of 8Gb RAM (note: for more than ~3GB you need a 64bit OS, else you will lose a lot of RAM between 3 and 4GB, and everything over 4 cannot be used anyway with 32bit)
This board is very similar to D2314 (only other EsprimoE form factor), so look here for supported CPUs and RAM types on D2314:
http://www.fujitsu-siemens.com/rl/perip ... ew_new.asp
Note: This is the website for the mainboards that FSC sells separately. I guess they don't list your exact mainboard there because it is a special form factor, and thus was not sold by FSC seperately. Just take D2314, it's the same board in uATX form factor