I've just finished downloading the 2.6.15.4 kernel and want to know how I can check which modules i'm using now to pass that information into the new kernel I am about to compile.

Run the command ' /sbin/lsmod '
Brian1

Did you compile your previous kernel yourself? If so, try the following:
- Run make mrproper in the new kernel source directory (possibly /usr/src/linux-2.6.15.4)
- Copy the .config file from the source directory for your previous kernel to the source directory for this one (possibly /usr/src/linux-2.6.15.4)
- Run make oldconfig
All of the other steps in building and installing a kernel still need to be followed. make oldconfig just parses the existing .config file and sets up the new kernel with those options.

If there are new options you will be prompted for those, you can also run make menuconfig or make xconfig, etc. afterwards if you want to tweak your settings.

No, I used th kernel that came with Debian testing, and thanks for the reply, and do I need any module for latinamerican keyboards, because some keys in mine doesn't work, they used to work perfectly, but after I reinstalled debian, they doesn't work, I already reconfigured xorg, and still nothing.

The previous post about running lsmod may be your best bet then - without a previous, manually compiled version of the kernel, the .config file won't exist.