Hi hotkey, welcome to NST
Deleting your Vista partition is probably not a good idea. W7 beta well expire August 1 unless you've got an extended serial which well only last a few months more, after which time you'll need to either buy the final released product or re-install Vista anyway. That being said...
Set your W7 partition as active in disk management: Right-click Computer -> Manage -> Disk Management. Right click Win 7's partition and select "Mark partition as active".
Now unhide hidden files, folders, and protected OS files on the the view tab in folder options: Computer -> Tools -> Folder Options.
Copy "bootmgr" and the "bcd" folder over to Win 7's partition from Vistas'. Reboot and if you can get into Win 7 still you're in good shape. If not, boot from your Win 7 DVD and perform statup repair: "Repair my computer" -> Select installation and "Next" -> Startup Repair. Statup repair may require 2 to 3 uses to fix everything.
Now that you're back in W7, use disk managemnt to reformat Vista's partition for whatever you want to use the space for or delete it and use the free space to extend W7's partition. Use EasyBCD to remove Vista's entry if it still exists and you should no longer get a boot menu when you boot the computer (should just directly boot W7).