Hi Aumfan,
I just bought a new embroidery machine (PE700) and trying to find answers to even the most basic questions can be frustrating.
I had the very same question because I always use the same bobbin thread as the top when I sew I assumed it was the same on embroidery.
Prewound white came with my machine, and yes you are able to use white or black bobbins and it is nit supposed to show on the top. I had a hard time trying to find a tension where my white bobbin did not come to the top. My thread would break often and regardless of what tension I tried I wasn't happy with the outcome. If you can pull your thread away from the needle after it is threaded and it will pull out your tension should be OK (does that make sense?. Setting my machine to a -2 tension stopped the top thread from breaking. I have read that some change the tension as they go but I am still in the learning process.
Practice with different designs as some are better digitized than others and may not be your machine that is causing the problem.
I bought PED basic and it does allow you to use designs created by others but you can not change anything. You do need the USB and the card to save designs to use so it is not a total waste. I bought Embird and it does allow you to make changes. It is not a total design package but $120 compared to $600 or $800 for a cheap design package.
I sent you an e-mail.
Rosa

Embroidery bobbin thread is often even finer than the top thread (like 60 wt), so there is less bulk. The prewound bobbins have lots of thread on them and are really handy. I got a box of 144 JP Coats polyester prewounds at a show a couple of years ago and I don't think I'll ever use them all!

There are some times, like when you're embroidering free-standing lace, that you want to use the same thread in the bobbin as in the top, but most of the time the black or white bobbin thread is fine.

Donna