Technically, Jim's textures garnered from his Truspace CD are illegal for anyone to use except Jim since he didn't license the right to distribute them. In most cases, what Guitta said is correct. When people are making freely available their own work, then it is okay to use it in your work. Some will add restrictions that it cannot be used in commercial projects; others don't have that restriction. The only way to be certain is to read the license information that comes with the download. :)