Vista Backup Centre

I just purchased a WD Elements Hard drive, is there any benefits to using their software (Memeo) versus just using the Vista Backup Centre?

I have a Dell PC with two harddrives (500GB storage - each) installed via the factory. My C: drive indicates 179GB free of 455GB; D: (DATAPART1) drive (i.e. backup disk) is now maxed out with only 10MB left of 455 GB. I also show an E: (Recovery) drive with 3.66GB free of 9.99GB.

Question: I need to reduce the size of the backup drive D: How do I do this and not loose data. I also don't understand how the backup drive can be larger than the size of my C: drive that it's backing up, unless there are similar (multiple) images on the D: drive that are the same (which doesn't seem very efficient and would explain why the D: drive is so full...).

Any help is appreciated.

Thanks
Kerry