Steam downloading a game.

You should be able to go to the downloads tab and just click the play button on both. The button is sometimes a little laggy for me though.

I can't download more than 3 at a time, but you should be able to download 2.

Steam is wierd sometimes I can download 3 or 4 games at once sometimes it only lets me download one at a time.

I think it mostly depends on your connection settings. For my connection (set for 2 MBps, although my connection is faster), it allows me to queue up multiple games for download but only downloads one game at a time (I just let it download when I'm off my system to minimize downtime).

There might be a case of where you can only download one PER DRIVE at a time, as it seems when I start chaining downloads to the same drive, it suspends the previous download while it parses the new download into the queue. However, when the download goes to a different drive (like J:\ instead of C:), it doesn't stop the download from the other drive.

Of course, your mileage will like vary based on your system configuration & internet connection.

You can set as many things to download as you want, it will simply do it's own thing in relation to order in which it downloads stuff etc.