To get the MC 19 installer to work I had to run it as Administrator. Something I didn't have to do on Windows 8.
Now that 8.1 is on MSDN and TechNet, I've installed it on my system. I'm also trying to run with a standard user account rather than an administrator account now. (the default account in 8 was admin, and I just used that)
I have run into a few issues caused by this—not everything behaves correctly when you use “run as administrator”—but I've not had any problems with Media Center so far.
On a standard user account, I
am getting prompted for administrator access to install MC19 - but I don't think this is any different from MC18 on Windows 8. If software is installing to Program Files, I think it's required.
So far, I have only had one piece of software that did not require administrator access to be installed, and it tried installing itself to "My Documents" instead of Program Files until I chose to run it as an administrator.
Most other software just fails if you deny it administrator access. I wonder if Media Center should try installing a portable version if the installer is not given elevated permissions.
To get MC 18 to uninstall, I had to reinstall over the existing install it as Administrator first. It would just error out otherwise.
There is currently a bug which requires you to run MC18 and accept the UAC prompt before you try to uninstall it, or it will fail. This is unrelated to Windows 8.1