Dual boot Vista XP failure

I installed Vista as the second OS, first was XP.
XP is on C:, Vista is on E:, checked the Vista bootloader
information and it contains the right entries.
The installation went fine, I reached the first settings ( region, currency etc. ) and the system
rebooted, but with failure.
From that point, when I try to boot now, the Vista bootloader fails and and the fallback to XP
gets activated, i.e. I end up booting XP.
It does not show me the initial choice of what to boot, it just says 'Failure'
and boots into XP.

Anything I could debug somehow ?

Thanks,

Wolfgang