I'm installing Gentoo from stage3, and whenever I do anything with a script like emerge, I get this error:
/dev/null: Permission denied.
The permissions on /dev/null itself are as follows:
crw-rw-rw- 1 root root 1
Any ideas?

just a shot in the dark:

maybe the group needs to be different??

on my slackware box it looks like this (group is "sys"):

crw-rw-rw- 1 root sys 1, 3 1994-07-17 18:46 /dev/null

I get the same messages in SuSE 8.2 Pro, both as user and as root. However, when I check the files I redirected to /dev/null, the file size is 0. So, I guess it works, and the error message is standard procedure, even when it works. Therefore, I don't worry about it anymore. In your case, check to see if user has permission to write to the file in question. If not, su to root, then do the /dev/null thing.
Since root has the necessary privileges, you might consider su to root before running the script which generates the error message. Otherwise, change the permissions on the script to allow user to execute the script.