Would windows 2003 Server 64-bit edition work well for video editing and sound creation?
IMHO, it (meaning Windows 2003 64 bit edition, not referring to AMD64 cpu's) would not work "well" -- At least not as of April 2004, it should work better in the future.
Older applications (32 bit) should run under 64 bit windows. However, many audio and video applications use specific cards for data capture and manipulation. Drivers for peripheral cards do need to be re-written, and it will be some time before many of the specialized cards will have native Windows 64 bit drivers.
You can find a partial list of drivers available for 64 bit windows AMD64 Device Driver Support for Windows® and Linux
I think the good news is that since the Intel EM64T are compatible with AMD64, you will see the more adoption of 64 bit windows by software and hardware vendors.