Well the graphics need to be done at some stage, so it depends on how nice you want your game to look. You will probably end up using basic programmer art placeholders while your game is taking off, but once you have a fair idea of what art you are actually going to need you can either make them yourself as best you can or try to get someone better at art to do them for you.

If you want to get someone else to do the art, then I strongly recommend you get a playable demo together first because people don't like to spend their time on projects that look like they are going nowhere. Just read through a few "artist wanted" threads in the the Help Wanted forum and you should get an idea of how to present your case, and what you need to have done already to not be flamed to death.

If you are doing them yourself then there is no problem really. Just put aside a big chunk of time and do the art till you are happy with it. There are loads of tutorials, free pograms, and artists forums around the web that if you want to you could learn to make quite decent looking art.

Good luck.