The GTAIV official website was updated with a PC section and some info in it, specially about the video editor.

? You can use it for SP or MP action
? The duration of the recording depends on the user settings and specifications

Check the official website for editor videos and screens.

That said, all the crazy content that will be created can be uploaded to the Social Club TV(will launch with Grand Theft Auto IV PC on December 2nd, 2008) and shared with the world, where the players will be able to comment and rate others works.

Also, the new player limit for the PC version has been confirmed as 32, and you can pre-order your copy as well.