The biggest servers int he world today are 512 GIG of ram... Those are $$$ servers and your friend would have to own two of them, and get them to work together then he could have a terabyte of ram. Cross hed be out of a few mill but thats besides the point.
No, it isnt dangerouse if you know what you are doing. Go read some guides, I would start with 99nasha's guide. That is a good guide for overclocking A64s. You will be able to do 2.4 pretty easily, maybe higher. It depends on your processor.