I recently purchased a Dual Xeon Server, and asked for 4GB ram upgrade by selecting the option in rs-account, but I was told my sever's memory limit is 2Gb, so only 1Gb extra ram is added, sounds like 4GB option is not available yet, is this true that current Dual Xeon Server can only add up to 2Gb ram, or there is a type of server that 4Gb ram option is avaible now.

I have a Dual Xeon which I upgraded to 4 Gb RAM recently. So it does work.

I believe Dell Dual Xeons can take 4GB while the non-Dell Dual Xeon (RS had them befor those Dell's) only 2GB.