How high a percentage of revenue are you willing to cede? Are you open to negotiation? Does that picture represent expected quality, environment, or both? When do you expect to work to be done by? Do you have an examples of other foresty scenes you'd like it to look like? Do you have a preferred style you'd like from the artist? Have you worked with an artist before? Have you worked with flash before? If so, how many cartoons have you done? What is the average batting average and amount of views your cartoons receive? Is the background to be suitable for the menu, or the cartoon itself? How long is the background to be witnessed in-flash?
Present any and all information up front. Keep your sentences short and to the point. Indicate all parameters in as little words as possible and keep all unnecessary comments - such as admitting that you think you suck, and emoticons- out of the message.
If you can bullet-point information, do so. Remember that you're hiring someone, and they expect as much from you as you do from them. Failing to indicate information isn't going to win you any favour. Good luck.