Why cant I send picture texts on my phone?

I bought the banter from alltel on a prepaid plan and I have unlimited text and free nights and weekends minutes. I cant send or recieve picture messages for some reason though, instead it goes to some website when I recieve one, but when I try to send one it won't even send. Even when I try to send the picture to my online-album it doesn't work. Can anyone tell me how to get my picture from my phone onto my desktop? I even have the card to put in the phone and then put in the computer, but my computer won't even recognize that the card has been inserted. I just dont know what to do. Can anyone help me?