the machine can still only see just over 3 of these 4 GB
You sure you installed Win 7 64-bit? Both 32 and 64 bit versions come on the same DVD. The 32-bit version of Win 7 has the same memory restrictions as 32-bit XP.
Does the BIOS report 4GB? If so, then most likely you have 32-bit Win 7. If no, then possibly the system can only address 3GB (unlikely, but not impossible).
SD