Yeah, that all looks as it should be.
You're going to have to do this the long way round then, I'm afraid.
If I were you, I would delete that .dmg file and try ONE MORE TIME (I know...) to download it again from the same source. I know it may seem incredibly unlikely given all the other problems you've had, but it could JUST be that the last download was nothing do with the previous problem. For the sake of 30 - 45 minutes it might be worth it (Because the alternative is going to take a couple of hours).
OK, assuming you've done that, and it still fails, or you're not willing to do it again, this is the long answer:
1. Re-read Thomas Reed's post above and follow his instructions.
If you don't know what that means, here's the full drill:
Power off the comptuer
Power on the computer, and hold down 'Command-R' immediately after hitting the power button.
The computer will boot into recovery mode. When you see a kind of 'desktop' screen, go to the menu bar and find 'disk utility'.
Open that and choose 'Repair Disk'.
2. When that's finished, exit back to the recovery desktop. From here, you have two choices: you can try booting up normally again (just hit the power button and 'restart'), or you can reinstall Lion (if you have an AppleID you'll need to enter that and your password, and it SHOULD reinstall Lion 10.7.4 for you. It'll take a couple of hours).
If you take the first option, you''ll still be in 10.7.1 or whatever you're on now, and you'll have to try the whole update process again. If it were me, I'd take the second option as its most likely to get you up and running in one hit.
Yeah you got it. Stop using any DL manager. If you have a normal, in todays standards, internet connection, which are fairly fast, you don't need any DL manager. Remove it from your system.