I had a difficult time setting this up myself but I think I finally got a working version that can puke out an flv with audio using ffmpeg and lame. Let me preface the fact that i'm pretty clueless when it comes to compiling. I searched for a couple days, came up with bits and pieces and after quite a few compiles, actually I lost count, I got one that worked for me.
You've obviously got ffmpeg installed:
clean the make for ffmpeg (make clean), and delete all the files that were created, or just wipe everything and start fresh.
I created a folder on root that would house everything for both lame and ffmpeg called "fmpeg". Hopefully this won't make things confusing.
(replace username where necessary)
install lame to 'fmpeg' folder:
i just uploaded the tar and extracted it to a folder called "lame".
cd to "lame" folder
./configure --prefix=/home/username/fmpeg --disable-shared
cd to ffmpeg folder and install to 'fmpeg' folder and configure with lame:
./configure --enable-mp3lame --prefix=/home/username/fmpeg --extra-cflags=-I/home/username/fmpeg/include --extra-ldflags=-L/home/username/fmpeg/lib
from what I gather cflags and ldflags are pointers to the lame include and library files that are needed.
also i get an initial "permission denied" when creating the config file no matter what the settings are, and when running the make it's strife with warning errors but i'm guessing those are normal?
upload a quicktime or something and test..
/home/username/fmpeg/bin/ffmpeg -i titleofvideo.mov -ab 56 -ar 22050 -b 500 -r 15 -s 320x240 test.flv
outside of the above I won't be much help unfortunately, maybe someone else can explain what all the flags mean.
if it works for you we should probably add it to the wiki or something.
Hope this helps some,