Try making a file called commandline.txt and put the commands in that and put it in the Grand Theft Auto IV directory. It's a lot more convenient imo.
@Rappo, try adding the following "-availablevidmem 320 -percentvidmem 100" and just replace the 320 with how much video memory you have.
The textures and models were not loading/spawning after I did the -norestrictions thingy and upped the resolution & detail levels, but adding those two commands seemed to fix it for me.
Edit: lol, I just read that the -availablevidmem is in GB.. either way, the commands I posted here work for me