I would like to share my experience with this, hopefully it will make someone's life easier. Note: Jump to the text in bold if you are only interested in what worked for me.
Initially, I copied all the files from the zip in the first post in my GTA folder (am using x64 windows 7, so that is C:\Program Files (x86)\Rockstar Games\Grand Theft Auto IV ). What happened is that the game crashed after the rockstar-logos intro. The XInputTest would crash also.
Then I tried the zip file in the 3rd (or 4th) post (the one that contains only dll files). The game was able to ran and the gamepad worked, but with no vibration. It also seemed like the dll is completely ignoring the ini file, because any changes I made in there weren't making a difference. I guess that's why vibration didn't work - cause it is disabled by default.
I managed to trace the source of the hack to this webpage and I found a newer version called x360ce_vibmod_3101_beta3 that is available here.
Now, remember. You need the file to be called xinput9_1_0.dll , NOT xinput1_3.dll. Download the file, put it in the gta folder and rename it to the proper name. Also, this version reads the settings from x360ce.ini , NOT xbox360cemu.ini . However, the x360ce.ini that is available at that last link is for some exotic controller, so what I did was I used the xbox360cemu.ini from the zip in the first post and renamed it to x360ce.ini .
My controller is speedlink sl-6535-sbk-01. The only modifications I had to make in the ini file from the first zip was to reorder the A,B,X,Y buttons like this:
A=3 #button id; 0 to disable
B=2 #button id; 0 to disable
X=4 #button id; 0 to disable
Y=1 #button id; 0 to disable
Hope this helps. Happy gaming!