These are the differences that I could tell between the "original" trailer and the just released one. Most of this info is from the quictime movie properties.
Video Size: Orig - 640 x 480 New - 320 x 240
Sound: Orig - 44.1 kHz, Stereo, Compression IMA 4:1
New - 22.05 kHz, Mono, Compression None
Besides being smaller, the new video is also darker.
Other differences include: RTCW logo at the end is different, "Comming Soon" changed to "The Blitzkrieg Begins this Christmas", and "Rating Pending" is now "Mature"
On a personal note, I think the new soundtrack BLOWS. It was one of the driving forces of the original trailer: pounding drums, wailing violins, just awesome stuff. The new music is simmilar but it sounds almost like someone tried to imitate the first but did it with MIDI instruments. I REALLY hope it's not indicative of what the actual game music will be (and I'm sure it won't be, unless they really plan to do it in 22.05 kHz and MONO)