Hello Thekiddotus,
To fix the "BOOTMGR is missing" error, try this:
1. Boot to the Vista installation DVD
2. Choose "Repair Your Computer"
3. Choose "Command Prompt"
4. Run "bootrec /fixboot" (no quotes). This will re-write the Windows Vista boot sector code.
5. Reboot - Vista will now start up normally.
Regards,
Raj