I want to put LFS on my 486. It hasonly 16M of ram, so I couldn't install my RH as a base distro. I then decided to use the only other distro that I have, FreeBSD 4.5, and I was wondering if anyone knows if using it would result in any difficulties, problems, etc. to install LFS.

P.S. if there would be, what would be a good distro to use, keeping in mind that I have only 16 megs of memory?

There are several ways of doing it. Try some search queries at http://search.linuxfromscratch.org

I used debian to install lfs on a 486 with 16mb of ram. I couldn't cross compile because the only other computer I had only an lfs install and it turns out there are problems cross compiling with an optimized lfs install. And I couldn't be bothered to install another distro on that computer.
If you are going to compile everything on the 486 then you are going to need a lot of patience. Make sure you have enough swap space too. I had a 100mb swap partition and compiling glibc it got up to 75% usage of the swap partition. My harddisk is very slow on that machine so it took about 24 hours to compile glibc with all the swapping going on.'
But now that I've got everything finished it's pretty fast for a 486 with only 16mb ram.