Ok...

Many thanks for LOTR for his help earlier, but i've got the issue.

Got so sick of having problems with all P2P clients that I went right into the guts of Windows, and to the Add/Remove Windows components panel.

Went through, and found that the Networking Components checkbox was grey, clicked details and found that P2P was unchecked.

I got all excited (as you do), checked the box, and proceeded to try and install the component.

BUT THEN:

I had the joy of this error message, halfway through it installing:

As usual, the error message is provided with MS's usual level of helpfulness and detail.

What can I do to get it to install? This is obviously the issue.

Cheers in advance,
Jamie