I know I'm doing something wrong here. I've tried to download the v 8.0.0 Co8 but the file that downloads is not recognised by my computer. However the 8.0.1 patch is shown as a recognisable file.

I've tried downloading the standard and the extra content versions.

Well the Co8 file is a non-compressed .exe file about 495 MB in size, so if that is not what's actually downloaded to your computer there might have been a connection error.

Circle_of_Eight_Modpack_8.0.0_New_Content_Edition_Setup[1]

Above is the name of the file. It doesn't seem to have .exe at the end. I've tried all the mirrors, it gave the same result every time. The file is 495mb.
The 8.0.1 patch did down load as a .exe.

Still very confused.

If you don't see an extension (.exe), then you most likely have the Windows default folders settings of hiding extensions. You can alter this in Folder options. The file should not have the suffix [1], though, so it may have been a repeat download, or a faulty download. Delete all currently downloaded Co8 files, empty your browser cache, and re-dowload them. The exact name of the files (with extensions) should be:

Circle_of_Eight_Modpack_8.0.0_New_Content_Edition_Setup.exe
Circle of Eight Add-On 8.0.1 New Content Edition Setup.exe

If you successfully re-download the files and Windows refuses to recognise the .exe extension, then you have a much more serious Windows registry problem that has nothing to do with these files. First things first, though. Try the above.

Definitely no 'serious' registry problem, lets not go too over the top!

Found out that only one of the mirrors seems to download a .exe. Typically it was the one with a poor speed, which is why I didn't go through with that in the first place.

Maybe the other downloads just needed a .exe extension adding to the file name.

Its all working fine now. Thanks to the help that was given.