Hi Leslie! I'd be happy to help. If you want to download any of the textures supplied by forum users for use as canvasses, you can right click on the image of the texture they've posted, then save it to your computer. Then when in ArtRage's paper settings ( assuming the Full Edition here ) you can click on "Grain", choose "load a file" and open this downloaded image.
If I'm misinterpreting what you're trying to do there just let me know with as many details as you can and I'll be happy to help you out there. Hope that's of some use1