Crossover cable length/verify errors

[dman]

I am going to buy a crossover cable in a couple of days for my big Xbox mod that I am prepareing to do(I'm going to use a NITC card). I read a tutorial that saids it needs to be short or else I will get verify errors. I haven't heard about this any where else, so is this really true? The reason why I am asking is because my Xbox is about 18 feet away from my computer so I want to get a cable approx. that size.