Patch installed, game works fine!
Here's exactly what I did, for anyone still having trouble:
1. Went to http://en.thewitcher.com/ee_manual
and downloaded Part 0, Part 1, Part 2
2. Moved them to the C:\Downloads folder (default location the installer uses)
3. Went down the page to "Enhanced Edition English Language Pack - 5 links" and downloaded 'Part 1'.
4. Moved 'Part 1' to C:\Downloads
5. Ran TW2EE_Patch.exe
Differences noticed so far: 'Enhanced Edition' has been added underneath The Witcher 2 logo on the main menu screen, in the Extras menu there's an option to watch the new cinematic, and the new lighting tweaks are in - better sunbeams and better light on Geralt's face. Also there's a very welcome addition to the options menu in the launcher, now you can disable the DLC bonus weapons and armour.