For editing sound, is it okay to plug headphones directly into the computer's sound out port? ie, will you be getting perfect sound by doing this? Or is some other bit of equipment (sound card or something) required to get the full signal?
I take it you mean the integrated sound board? if so, dear lord no! These things are the bain of my college life (my college is too cheap to buy real sound cards...). what you hear through them bears very little resemblance to what's actually there.
Or a decent firewire audio interface. I've got a m-audio usbpre that is fantastic and gives me two xlr inputs with some nice outputs as well. And I can take it anywhere and plug it in. Has proved itself quite handy. The case feels a bit cheap and lightweight but I keep it in a padded laptop bag and havent had a problem.
Another question, so I don't have to make another thread for it.
Is it possible to use a splitter so I can have two people listening to the same signal on headphones? Something I can plug into the camera's headphone jacks that has two outputs. Something like this.
You shouldn't have any problem using the splitter - just don't forget to get an extra long extension cord for the sound guy's headphones - he won't be that close to the camera most of the time.
There are a lot of other options for getting sound to the boom op - I personally use wireless (Comteks - well, ListenTechs really, but close enough). In my current setup, I have the boom op on a different channel than the other ListenTechs so I can better communicate with him/her without everyone else hearing.