i have the 5.0 book printed out, and my question is whether i should either
a) print out the 5.1 book (which has the boot cd i'm looking at)
b) use the 5.1 boot cd with the 5.0 book
c) use the 5.0 sources with the 5.1 boot cd

you can do any of the 3 options but i would reccomend option c with option a

I think you can use things from the two books, like I did..

For example, the 5.0 book uses GCC 3.3.1 and I used GCC 3.3.2 that's stated in the 5.1 book, and so on with some packages like perl or some other packages...

What I mean is I used the instructions from the 5.0 book but using some packages from the 5.1 book, and it worked perfectly for me, so you can use the option you want, just having in mind you must follow the instructions on the book... The only criteria I applied for using a certain package or not was stability... I wanted a stable LFS so no unstable/testing packages came to the compilation... in your case, do what you consider better for you

Julio