From what I know, 1.17c is optional, and in my case in past I was not able to install it on windows XP. The most of things are fixed in 1.17a so maybe that is all you need. Once I went to windows 7 it was easy to install. Keep on mind that you need to install first 1.17a before going with 1.17c.
For more info and instructions contact Malgardian.

I just ask because I used Patchfix earlier on the same machine with WinXP on it and it worked like a charm. Then I installed Win7 there, got bored with its clunkiness and reinstalled WinXP with the same set of additional software as before, including all possible .NET and C++ versions, and now the Patchfix refuses to run. It looks strange.

Yes, I do know it's optional. And it can be installed manually anyway, though it's a kind of chore. Maybe, it would be the only option for me though.