The tool is there for you during the editing handling.dat easier.

It's compatible with the latest Version of GTA IV 1.0.4.0.

It supports also four different languages like german, spanish, italian and russian.
I translated it with google so sorry if there are some misstakes.

For all XP users:
If an error pops up, like uxtheme.dll is damaged. You will need this:
http://www.chip.de/downloads/UXTender-UXTheme-Service-Patcher-for-XP-SP3_31636544.html

Have fun!