I believe you will need to use WinPE to do the install of 2008 and we don't support a WinPE installer until 7.4.x. Official support for provisioning Windows 2008 was added in either 7.4.5 or 7.5 (check the release notes).
If 2008 can use the 'unattend.txt' method of installation, it may still be possible w/ our DOS-based provisioning in 7.3.0, but you'd probably have an easier go w/ a newer version of BladeLogic. And w/ 7.4.x we can do x64 versions of Windows, which you cannot do w/ 7.3.0
The 2k8 installer requires a 32-bit environment at a minimum which is typically achieved via WinPE. The 64-bit WinPE can initiate a 32-bit install, but not vice versa. So, this also rules out the blade.img approach to initiating 2k8.
At a minimum, you'll need release 7.4.5 I think? I'm not 100% on that, but it's definitely one of the later 7.4.x releases. I'm still trying to track this down.