One of the big questions about GTA IV: San Andreas is whether or not it support everyone's favorite digital distribution platform, Steam. Without beating around bushes and skipping over dead horses, the simple answer is: Yes, GTA IV: San Andreas can be played either with the retail version of the game or via the Steam version of the game.
To answer another question, no you cannot play GTA IV: San Andreas on the home consoles. It's unfortunate yes, but that's the price you pay for a closed off, secure system.
Anyway, the Rockstar Mod Studio released a showcase of all the features for their recently released mod. The mod itself does not yet support full mission scripting to replicate the missions as they were in GTA: San Andreas but given how the team managed to port over the voices, all the radio stations, the weapons, vehicles and a few of the activities, I wouldn't discount the team for one day being able to port over all the missions as well. Check out the features in the video below.
Now the main thing is that a lot of gamers are curious just how well the Steam version of GTA IV supports a mod of this sort and given that most mods install with no problem, you should have no problem getting GTA IV: San Andreas to work (especially if you already run other mods just fine, such as complex scripting mods or map modes)
As usual, though, make sure that you're installing GTA IV: San Andreas on top of a clean install and that no other mods, hooks or scripts are active, otherwise I imagine there could be some problems. The mod is also compatible with Episodes from Liberty City so you shouldn't have any problems there.
You can check out the official GTA IV: San Andreas website for further support or more information regarding the mod.