Installing SoC right now, and I keep getting this error message:

"an error occurred while trying to copy this file:

not enough storage is available to process this command."

It popped up for other gamedata files (db2, db4) but those went away upon hitting 'retry.' This one keeps popping up right away, though.

Well did you check if you had enough space for installing it on your harddrive? Please note that if you install it on other partions/drives than C: you still need enough temporary space there (around 6GB in case of Stalker SoC) to be able to unpack the data temporarily - and that is happening during install ;)