The two episodes will available in two different ways, much like they are on the Xbox 360. GTA IV owners can opt to download the episodes individually from the PlayStation Network or the Games for Windows Live Marketplace. Users looking for a standalone package can grab Episodes of Liberty City, which collates the two installments on one disc. Given current prices for the 360 versions of this content, it seems likely that the individual episodes will run $20 and the Episodes disc will go for $39.99.
The release also mentions that PC players will receive an "advanced video editor" with these add-ons, but it isn't clear if this means that it's advanced beyond the video editor that's already included with GTA IV on the PC, or if Rockstar is just claiming that its existing editor is, you know, advanced.