Are there any Speilbergs out there who can help me?

I've been transferring digital video footage (tape) onto my computer, but the quality deteriorates big time.
(Crystal clear when I hook video camera directly to TV for playback, terrible when I load it onto the computer)

I use a DV cable and windows movie maker.
Is either one of these the problem?

If WMM is the issue, what software programs are better?