I've got it working perfectly. There wasn't much information on the windower forums, but with a little trial and error I figured things out.
First, download the zip file on the linked page in the OP.
Second, once you've extracted everything, place FFHook.dll in the Final Fantasy XI folder on your harddrive. Then, place the MadChook.dll in your PLayonline Folder on your harddrive.
Edit:
Okay, I seem to have caused some confusion as to what I meant by "place", what I meant was copy/paste the .dll's in the right folders, because they also have to be in the windower folder for it to work at all. Hope that clears up some problems.
Then, go into your .ini file and change the Usepixelshader and Regkey values to look like this:
UsePixelShader=0
FilterA =0
FilterR =0
FilterG =0
FilterB =0
PolRegKey = SOFTWARE\PlayOnlineUS\InstallFolder
# for US client(?)
#PolRegKey = SOFTWARE\PlayOnlineUS\InstallFolder
PolRegValue = 1000
Of course, if you're using EU or JP playonline it would probably look more like: SOFTWARE/PLayOnlineEU/InstallFolder, or JP, or whatever. Depending on what version you use.
To start up the windower you use the FFhooklauncher.exe. POL should start up and when you go in game it'll be windowed.
To get Cell shading:
Look up at the top, there will be three options (No idea what they say, it's all in JP for me >.>).
Select the second colomn from the left, then the third option down from the top.
That should be your cell shading.
If that doesn't work randomly click on shit until it does.
Disclaimer: I don't know how to read japanese, nor do I know if this will work for you. I figured all this out by trial and error, but I believe you should be able to get it working just like me. I take no liability if you wanna try this and it screws up your system. After all, I have no idea what I'm doing.
Screenshot:
http://i32.photobucket.com/albums/d39/Lecan/2005_12_03_17_00_33.jpg
Edit: And also, just so you guys know I'm running a GeForce FX 5200 with the 81.85 drivers, so if Cel Shading doesn't work for you it might be that you're using drivers too old (Or at least that's what I speculate).