Snow leopard startup freezes at grey screen

My Snow leopard machine hangs during startup at the screen with the Grey Apple logo. It appears there is a SW issue with my OS X boot partition. Here are facts I have learned:

• The computer boots fine if I hold option at startup and select my boot camp partition
• The compute boots fine if I attach an external HD with OS X 10.6
• Running a disk repair from the external HD, I see the following two issues that are repaired. Also, note the last line about boot partitions
• 
• After this disk repair, the disk will still not boot, it hangs at the Grey Apple logo.
• Booting in safe mode does not resolve the issue, the machine will still not boot to a desktop
• Booting in Verbose mode, drivers initialize with the last succesful line being the ethernet drives (I believe) and then the hangup occurs. It is unclear what state the boot process is at on the hangup.

This situation has happen twice in the past few weeks. The first time I did a reinstall of OS X to resolve the issue. Then, the issue appeared again approximately two weeks later. I'm hoping to avoid a second reinstall (And really, avoid this issue in the future).

Any thoughts on what is happening? It seems perhaps something in the boot partition table or the OS partition, although disk utility says the partition is fine. I have downloaded Test Disk 6.13 to look at the partition table, but I don't know how to interpret the outputs of that program.

Any help appreciated.

Thanks,

Josh