I don't know about jQuery but in general terms I can think of a few alternatives.
- Use isometric tiles to create the background. It's very similar to creating a top-down tile based map but with tiles being offset a little. You can find more information here.
- Turn a top-down background into isometric by rotating 45º and compressing it vertically, either in code or in some image manipulation software.
- Probably not applicable here but in a 3D API you can also get an isometric view of the world by setting an orthographic projection and positioning the camera at the correct angle.