In order for a system to see and utilize 4gb of memory or more you need to run a 64 bit operating system... Also your motherboard must support that amount as well.
32 bit o/s will use 3gig of ram if you want to run more than that you will need a 64bit o/s
tell your friend to right click my computer and select properties and he will see just how much of his ram the o/s is using.