Backup programs are notorius for causing problems on restore. Since you have an external hard disk why not just clone the disk. I have all 5 (three desktops and two laptops) of my PC's hard drives cloned. Every so often I just make a new clone. In case of a failure I just swap the drive. Any other "stuff" that's new can go onto a CD until it's time for a new clone.
I've just done a backup, on my Dell Inspiron computer Vista Home Premium) using Windows Backup and Restore Centre, to an external hard drive (F). However, when I tried to check using the Restore function, that drive does not appear - only C and D (recovery) are shown.
This doesn't fill me with confidence in the function. Perhaps I'm doing something wrong, But I'd hate not to have myself covered.
(In My Computer, the F drive is shown.)