If I download the samples from Clipartopolis.com, what format would be the best for me to download so that I can try to digitize with Artista Designer Plus, Version 4? BMP and...???

The manual might tell you which format the software accepts. Mine can handle quite a lot, but I usually download .bmp and .jpg

There is no limit so if i were you, i would download in .wmf; .jpg; & .gif
That way you can try them all and see which one works best for you. hugs n roses, Meganne