Some of the people who downloaded yesterday's Homeworld 2 mod preview had trouble getting the file to install and run. Aaron has looked into it and created a fixed version. It's already replaced the original file online here. If you downloaded the package from the CIC prior to this afternoon and the program doesn't seem to work, make sure you have Homeworld 2 version 1.1 installed. If it still doesn't run, L.I.F. created this workaround you can try:
Move wca.rar to Homeworld 2's "data" subdirectory.
Create a shortcut to run Homeworld 2.
Right click on the shortcut and open up Properties. Change the Target to: "C:\Program Files\Sierra\Homeworld2\Bin\Release\Home world2.exe" -mod wca.rar (you may have to adjust this if the game is installed to a different directory)