[CentOS] Really Weird Question.....

So I just got ahold of an old e-Machine (Model EL1600) with 1GB of memory. I was going to install CEntOS on it and try to run VirtualBox for other OS'es. I am curious to know if I have to stick with the 2GB "max" the specs say the machine can take or if its possible to install a 4GB module that is designed the same? In other words I have seen 2GB DDR PC2700 memory that will fit the casing and work, but I have ALSO seen 4GB DDR PC6400 memory modules with the same number of pins (240) will this work? I would want to have as much memory in there that will allow the VirtualBox to run smoothly.....any help would be appreciated!

EGO II