cam to pc = too dark

i have a sony digital 8 camera, it has an input so i usually record music videos on, it uses usb to record them on to the pc, i got an 8 mb memory card with it that can save a few 15 sec videos,
now the memcard videos are very good , where as the stuff i try to record from cam to pc turns out rubbish, too dark and not great quality .
i got a program called Pixella with it, ive tried unlead something and windows movie edtor.

would ther be ne way to increase that 15 sec, i tried a 16 mb card, no diffrence.

Thanks