In order to quickly compile your  libx264, you can type the following commands in your shell:

# cd /my/path/where/i/keep/compiled/stuff
# git clone git://git.videolan.org/x264.git
# cd x264
# ./configure --enable-static --enable-shared
# make
# make install
# ldconfig

P.S. If you are using Ubuntu, you'll most probably have to use sudo for the last 2 commands, like:

# sudo make install
# sudo ldconfig

P.S.S If you get a message like this:

Found yasm 0.x.x.xxxx
Minimum version is yasm-1.0.0
If you really want to compile without asm, configure with --disable-asm.

that means that you have an old version of yasm on your system, so you should update it. The quickest way to do so is like this:

# wget http://www.tortall.net/projects/yasm/releases/yasm-1.2.0.tar.gz
# tar xf yasm-1.2.0.tar.gz
# cd yasm-1.2.0
# ./configure
# make
# make install

and after that, just repeat the configure/make/make install steps for libx264 and it should be fine this time.