I am not very happy about the lack of information related to that in the Fujitsu-Siemens laptop computers. I bought a xi1526 (a more than 1000€ computer) thinking of upgrading its RAM memory to 4Gb, which is the only limit that appears in all of my laptop's instructions. And days ago, when I bought 2x2Gb kingston 667MHz modules, I am surprised due to the fact that it is impossible to start my computer with more than 2Gb! I am not talking about Windows XP limits or similar, I am talking about a total black screen. Not SO, not BIOS,... nothing. Only a beep, possibly due to a motherboard that will never support 4Gb or a bad BIOS program (I have tried to install the last upgrade, I have tried starting with each one of the modules separately and in each of the two memory slots, and all was perfect with 2Gb. and, of course, I have checked in forums that I was right, the laptop does not support it).
And probably, some people know that it is not only a Fujitsu problem but an Acer, Asus (at least some types of G1 does not support 4Gb! Incredible!),...
Now, I have been trying to contact the Spanish telephone assistance for more than half and hour in total, making calls of 2,5,6... minutes at different moments, but the number of lines are insufficient, all collapsed.
I feel totally cheated about that stuff. And now, I am not thinking of waiting a solution cause I know that It will not be. I only can give this valuable advice to the ones that, like me, does not know about that important limitation when the 4Gb laptops are arriving.