You can use them, no restrictions(from me at least, some of them I just collected from random places

)
I made a tutorial on how to make the textures tileable.
Heres the link.
http://www.coniserver.net/ubbthreads/showflat.php/Cat/0/Number/664609/an/0/page/0/gonew/1#UNREADIts compressed with a program called winrar, you can get it from
http://www.rarlab.com/