If you are playing using backwards compatability on the Wii, then yeah definitely get it hooked up via component cable as a first effort. I found this to be a huge improvement over composite, and the horizontal line issues you are referring to may very well be related to your tv's handling of the deinterlacing.
edit: oops, your issue is with vertical lines. nvm my post... well aside from the fact that component cables are a good investment even if it doesn't resolve your line issue.
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