You can get long DVI cables, but they are VERY expensive beyond about 10' in length. I use 10' ones myself and they work flawlessly at my current 1280x1024 resolution.
As for VGA cables, if you get properly shielded cables, you do not need a booster. I have one 25' VGA cable that produces a nice image (as good as any 6' cable) at my 1280x1024 resolution at 75-85Hz. It might do well even higher, but I haven't tried.