Depends on what resolution you created it at... If I were going to use non-vector art, I'd probably shoot for 300 dpi for the artwork, but I think I've read some people say as low as 150 will produce acceptable results. If you created your artwork at a lower resolution than that, you'll have to redo it at a higher resolution. There's no real way to scale up low resolution artwork and have it print well - that's why the vector art is so popular around here.