Guess kernel configuration from built kernel

Hello,
I reinstalled gentoo in my computer and I didn't want to recompile the kernel (recompiling wasn't itself the problem, the problem was configuring it before...). As I had a /boot partition, just left it untouched and then everything worked fine in the reinstall. I downloaded the gentoo-sources but didn't configure it. Now I need to compile madwifi (which needs to be compiled against a kernel configuration) - but paludis gives me erros because of that. Is there a way to make a kernel "config file" from an already built kernel?

Thanks in advance =)

Can you see /proc/config.gz ?

Sorry for not updating the post:

I was able to see config.gz. Looked for this hint really hard and found some chinese forum which explained (this part in english) how to get this config.gz (I was trying with a script, but couldn't get it to work). I got it and loaded the config file in "make menuconfig" but the configuration was just the same, couldn't reload it. Then I just recompiled the kernel anyway =/

But thanks a lot, SteveL ;D

OK, so just to make sure you did the right thing with /proc/config.gz ...

cd [directory of your kernel source]
cp /proc/config.gz oldconfig.gz
gunzip -d oldconfig.gz
[that should get you a plain text file full of "CONFIG_item=whatever" lines]
mv oldconfig .config
make oldconfig [or whatever make target you are aiming at]

I did almost that. instead of make oldconfig - make menuconfig and inside the menu I've chosen to load an alternative configuration file - then I pointed to the copied file.