I need to have all attempts to one URL (old_domain.com) re-direct to a new URL (new_domain.com) the sites are on different hosting companies (neither of which are godaddy), but godaddy manages the DNS for both. Is it as simple as editing the DNS for old_domain.com and putting in the same IP address as the new_domain.com? If not, what do I need to do?
One very simple way to accomplish this is to "forward" your old domain to your new one. Go to your DNS settings for your old domain. The forwarding dialogue box is found under Domain Settings. About halfway down the page you will see a box for forwarding. Click into it an follow the prompts. I recommend "forward without masking."
Depending on how your server company configures their servers and what software you are running, just adding an IP address might not work well in all cases. Their tech support should be able to tell you if it will work on their server. Some hosting companies require a CNAME as well as an A record.
Hope this helps,