It really probably depends on you exposure to computers, programing etc. If you already use a structured language, moving to C shouldn't be too challenging. There are resources that are fairly good
http://www.duffin.org/books/c/
http://www.cyberdiem.com/vin/learn.html
There were two books that were instrumental for me when I was learning (both are available at most b&n/borders/amazon):
1. The C Programming Language by Brian Kernighan and Dennis Ritchie (the creators of the language)
2. The Standard C Library by P. J. Plauger
Cheers,
Keith