Guy N'wah:
I want to see mine completed and working before I say this is the correct step-by-step. But so far, this seems to work:
If you get the error on pack0.dzip, select "Abort". Don't "Ignore"; you'll waste your time and get a broken game.
Get the correct Part 2 file (TWEE_Patch-2.bin) from this page: http://en.thewitcher.com/ee_manual/ Place it in the same folder as all the other parts, overwriting the old incorrect Part 2 file.
If after you abort the patch, your Launcher is broken, uninstall the game. The uninstaller allows you to preserve your saves; do so if you want to keep them.
Reinstall the game, then start the Launcher.
You should get a dialog offering to patch the game to EE. Click through until you get to the dialog where you select the patch location.
Set the patch location to the folder above the Downloads folder; for example, if your downloads are in "E:\TW2EE\Downloads", select "E:\TW2EE". The downloader will append the "Downloads" folder to your selection.
Select the components (the main patch and any language packs) you want to install.
Now the downloader will ask you where the game is installed. It should get the right folder by default.
Then it asks you again which components to install. Select the components you want.
Click through, and the patch will install.