I'm going to try and document any issues I have while attempting to get warhammer online installed under linux with wine.
My first problem came because I was trying to install on /media/stuff - this is a different partition since my / (z:) drive was nearly full. Since wine doesn't update free space, and z: was almost full, I had to create a symbolic linl to the other directory.
Second problem came when attempting to choose a folder within now s: (/media/stuff) - I could only get the "The install folder is not valid" error message - in order to work around this error, just remove all the extra stuff after your path and make it warrhammer. I have a feeling it's either the spaces ' ' or the dash "-" that was causing the problem. In my case the final path was s:\games\warhammer - this then allowed me to click the install button.
I was then able to launch the game file - it downloaded some patches and restarted the game. After the game restart it asked for the user/password of the registered user and started downloading more files.
One item of note - the check boxes and other text on the patcher screen is not textured. I'm not sure why and can cause a number of flickering issues while the screen updates.