ubun2

I had windows vista and ubuntu 9.04 on my machine. Ubuntu has installed grub boot menu and it automatically detected windows vista installation and added it to the grub boot menu.
 
Now i installed windows seven and looks like it screwed up the grub boot loader. When i boot all i see in Windows Seven and Windows Vista from the boot menu (this is not grub boot menu). It is the windows boot menu. Now I can't even access or boot to my ubuntu.
 
How to fix this so that i can get my ubuntu back?