Sometimes. There are distinct advantages and disadvantages to writing solo or as a team. You will have to communicate a lot if you choose to write with a partner, and you may have to compromise a little on storyline, but you will have someone to bounce ideas off the whole way. Writing solo, you can write whatever you want whenever you want, but are responsible for the entire page-count goal yourself.
You can choose how many words you want to try to write when you register. If you're writing with a partner, up your word-count goal a little.
