Just a FYI in case anyone else had the same problem as me.

For whatever reason when I downloaded an .iso from FTP or HTTP sources linked to from the debian.org website every one of them failed when I went to install it.

I downloaded a bunch of different version; businesscard, minimal install, i386 and AMD64 versions. When I tried the i386 and AMD64 version (network install failures were my fault) I go errors during the base install that said a cerrtain package was corrupt or unavailable, I forget the exact wording.

All MD5 sums were checked before and the CDs were checked too, one CD checked came back as defective during the CD check test, I did the CD check after a failed install MD5 was before.

In the end I used jigdo to download an .iso and it worked fine.