I have installed these OS's in this order:

1 - Vista
2 - Ubuntu Server 9.04
3 - Ubuntu Desk 10.04
4 - BT4

I recently upgraded my most often used OS (#3) to 10.04 version and it updated GRUB to GRUB2 as part of the dist-upgrade.

I have a feeling that I wasn't careful enough when installing BT4 or I made a mistake in the partitioning. I had plenty of space that was free waiting to be used by some other os and I designated some of that space for BT4.

The Issue
When I got it all installed (off of a USB live boot) I rebooted and noticed it was back to grub one. The Vista install and the Ubuntu Server install both work still... but the recently updated (to Grub2) Ubuntu Desk install now hangs immediately after selecting it and pressing enter in Grub. I can mount the partition within BT4 just fine and see that all my data is still there, it just won't boot.

What I've tried
Using BT4 to install Grub2. (no luck)
Installing Grub1.5 back after finding Grub2 didn't work. (no luck)

My plan
When I get home from work today I'm going to take the "quiet" option off of the boot command in Grub for that Ubuntu OS and see if there's any error it's dumping before it hangs.
Hope that someone has had this issue before and can just tell me a straight forward way of resolving this issue. I'd prefer to use GRUB2 as my boot loader.

Cliff Notes
Had other OS's installed
Updated to newest Ubuntu (installed GRUB2 as the new bootloader)
Used some spare disk to install BT4
New Ubuntu that used Grub2 is now the only OS that won't boot

Any help is greatly appreciated, and I will post any information that anyone may need to help me get this resolved.