"Command & Conquer: Gold" and "Command & Conquer: Red Alert" have been released free in the past, I guess in conjunction with a sequel being released. Now that "Command & Conquer 4" is coming, you can now download even more for free!
I've retrieved the headers for each of the files, and the values given by the servers are as follows:
Command & Conquer: Tiberian Dawn (GDI) = 608987136 bytes = 0.57gb ISO
Command & Conquer: Tiberian Dawn (NOD) = 592476160 bytes = 0.55gb ISO
Command & Conquer: Red Alert (Allied) = 524014608 bytes = 0.48gb RAR
Command & Conquer: Red Alert (Soviet) = 526433084 bytes = 0.49gb RAR
Command & Conquer: Tiberian Sun + Firestorm = 1334180630 bytes = 1.24gb RAR
Total = 3586091618 bytes = 3.34gb
Burn each of the ISOs using your favourite program. I've been using ImgBurn ( http://www.imgburn.com/ ) for many years now because it's 100% free and works exceptionally well.
Alternatively, you can mount the ISO directly without burning by using a virtual CD/DVD program such as Daemon Tools Lite ( http://www.daemon-tools.cc/eng/products/dtLite ). Again, I've been using this program for many years with no problems whatsoever.
Enjoy :)
Apparently C&C: Tiberian Dawn is the original game, so I assume C&C: Gold and C&C: Tiberian Dawn are the same title. I've removed the link to Gold in the original post and put it here as an alternative mirror :)
Command & Conquer: Gold - http://ccgold.ea.com/uk/
Sorry for any confusion.