Check your BIOS for an entry that will relocate your video ram (goes by different names). Some motherboards can't do it though.
By default the video ram does sit in the lower 4 gig. Having a 64 system means you can have more than 4 gig of ram installed, but doesn't get you around the fact that your hardware may still need to use[/edit] still block some of it.
Even if you can relocate your video memory above the 4 gig line, if you have 8 gig in your machine it may still show up as a hole... again, motherboard/BIOS dependant.
BTW that bar graph doesn't give you the relative locations of those memory usages, merely the amounts in use... The hardware hole is not at the begining of the ram it's most likely on the 3-4 gig. mark