White MacBook hangs at gray Apple screen forever, won't boot to single user, won't mount using Disk Utility. What do I do next? After a forced shutdown, my white MacBook hangs at the gray screen with the Apple logo and an infinitely spinning progress wheel.

I can boot in verbose mode, but I didn't see any particular error, just a timeout (I can provide the verbose text, but I'm at work and my Mac is at home).

I can't boot into single-user mode. It just sits at a similar point as the verbose mode.

I booted off my Snow Leopard install DVD. It took nearly 10 minutes! Once it got the install screens, I ran Disk Utility. It sees the internal hard drive. It sees the partition. Info on the partition shows that it is an HFS partition. But, it's grayed out and unmounted. If you click "Mount" it says that it cannot be mounted - run First Aid.

"Verify" runs for about 8-10 minutes, shows messages for each step, no errors, and then says Verify has passed. Still won't mount. "Repair" runs for about as long, shows no errors, shows no repairs. Still won't mount. Grrr.

I hooked up an external drive and created an Image of the drive. This took hours. Completed with no errors. I then tried to mount the disk image (.dmg). It ran a full Verify (I don't know how long - I fell asleep). It Verified, but said it couldn't be mounted and suggested I run First Aid. Verify passed. Repair is grayed out. Won't mount.

What should I do next? I'm going to replace the hard drive no matter what, but my last Time Machine backup was 7 months ago (I know, I know, ...) and I would like to, hopefully, get to the last 7 months of files.

It's the only Mac I have, so I can't do the Target disk thing.

DiskWarrior? Any other utilities (particularly free ones) to try? Bootable Linux utilities?

Also, assuming file-system corruption, could my external disk image be processed by disk utilities just as easily as the hard drive? In other words, if I erased my hard drive and repartitioned and reinstalled the OS, would I be any worse off in regards to maybe recovering files if I just deal with the external Image? 

Otherwise, I'll probably replace the internal drive, reinstall, then but the internal drive in an external SATA-to-USB enclosure and work on it from there...
When this happens to me, I've found that resetting the PRAM/NVRAM often works.  (Sometimes it takes a couple restarts to see any results.)

Also, if you haven't already done so, take a look at Apple's troubleshooting steps for this problem.