Vocal Sample For Critique

I'm not sure if you were listening to the song and singing along, but I think hearing the relevant harmony would help the pitch problem. Singing unaccompanied is very, very hard, so stay away from that for now. I would recommend singing along to a keyboard if you have it, or any other fixed pitch instrument.
This sounds like you are expending a lot of effort, and I think it is has to do with the range. It sounds a bit high and nasal, so I would highly recommend singing it in a lower key. That would also help with your breath control. You seem to run out of breath on some sustained notes and then take a big gulp, which is not ideal. It's hard to convey this on the internet, but carefully marshaling your breath will make for better sound. Be sure to have an erect posture when you sing, and keep your diaphragm engaged--you should feel some slight muscle tension in your upper abdomen. Once you get this, you can take a very short breath and fill your lungs for the next phrase or few. Another important tip is to "breathe low"--your chest should not puff out when you breath in. Lie on the floor and take a deep breath and you will see that it's your stomach that puffs out.

Sorry for the barrage of vocal technique stuff that probably sounds confusing, but in summary:
sing with accompaniment
think about breath control
sing in a lower range

I just uploaded an mp3 of Dolly Parton, Linda Ronstadt and Emmylou Harris doing "After The Goldrush". I absolutely LOVE this version! It's a very good one to sing along with!! You can find it here. When I do this song I change the lyrics from Neil's original "in the nineteen seventies", which Dolly and Linda and Emmylou changed to "in the twentieth century", to "in the twenty first century" just to bring it up to the current time! :D

As far as your voice, yes, you do need some work, but I hear a good foundation! Breath control is very important and, once you get that a little better under control, those notes that you're struggling for will come more easily. Don't just use the breath from the top of your lungs. You've got to feel it all the way down into your stomach. I'm sure you've heard the phrase to "sing from your diaphragm". Keep singing and build up those muscles! The more you sing, the stronger your voice will become!!

I agree with Sam that you're trying to sing out of your current range. Find what feels (and sounds) good without having to struggle for it. If you're hitting flat notes on the high end, try it in a lower key. If you're having trouble hitting the low end, capo up and sing in a higher key. (I play "Goldrush" capoed at the third.)

My advice would have to be the same advice I give for guitar.... Practice, practice, practice and then practice some more! :D

A part of the problem is that I'm sitting down because I do this song with guitar and I usually sit down when i'm playing. The other part of the problem is just playing and singing. I keep trying to play and sing but one loses out to the other unless it's a simple strum song.

And I've heard the version you spoke of. I like it too.