Edit:
We have now a temporary git repository at gitorious:
http://gitorious.org/replicant

== Before starting ==
 * Root your phone
 * Backup your current system!!!
 * Install git

== Setting up the build environment and getting source code ==

These instructions assume that you are building replicant in your home directory (~).  If you are building it in another directory, modify path names accordingly.

=== Get the repo tool ===
repo is a front-end to git which is used to manage several git repositories.
{{{
 mkdir bin
 cd bin
 wget http://android.git.kernel.org/repo
 chmod a+x repo
 cd ..
}}}

=== Check out the Replicant repository ===
This step will download the Android source (minus the kernel) and the Replicant patches.
{{{
 mkdir replicant
 cd replicant
 ../bin/repo init -u git://gitorious.org/replicant/manifest.git
 ../bin/repo sync
}}}

== Optional: building the kernel and wireless LAN driver ==

By default, the Android build system uses a pre-compiled kernel and wireless driver rather than compiling these components from scratch.  If you want to compile your own copy of either of these components, you have to compile both: the wireless driver sources included with Android are incompatible with the pre-compiled kernel.

=== Get the kernel source ===

To download the kernel sources, create a file in your replicant/.repo directory called "local_manifest.xml" containing the following:
{{{
<?xml version="1.0" encoding="UTF-8"?>
 <manifest>
  <project path="kernel" name="kernel/msm" revision="refs/heads/android-msm-2.6.27"/>
 </manifest>
}}}

Then from the ~/replicant/ directory, run:
{{{
../bin/repo sync
}}}

This will create a directory called replicant/kernel and download the kernel sources to it.

=== Build the kernel ===

To build the kernel:

{{{
cd ~/replicant/kernel
export ARCH=arm
export CROSS_COMPILE=arm-eabi-
export PATH=$PATH:~/replicant/prebuilt/linux-x86/toolchain/arm-eabi-4.2.1/bin
cp arch/arm/configs/msm_defconfig .config
make oldconfig && make
}}}

Wait several hours.

=== Point the build system to your kernel ===

Create a file called `~/replicant/buildspec.mk` containing the following:
{{{
TARGET_PRODUCT:=htc_dream
TARGET_PREBUILT_KERNEL:=kernel/arch/arm/boot/zImage
}}}

This will instruct the build process to use your kernel rather than the pre-compiled kernel.

=== Build the wifi module ===

To build the wifi module:
{{{
cd ~/replicant/system/wlan/ti/sta_dk_4_0_4_32
export KERNEL_DIR=~/replicant/kernel/
make
}}}

(If make can't find your compiler, re-run same PATH export command you ran before compiling the kernel.)

Replace the pre-built wifi module with the one you just built:
{{{
cp wlan.ko ~/replicant/vendor/htc/dream-open
}}}

== Build the firmware ==

=== Change the build scripts to include some important missing packages ===

''(This section will be removed once these changes are committed to the replicant repository)''

Open the file {{{~/replicant/vendor/htc/dream-open/htc_dream.mk}}} and at the following text to the beginning of the file:
{{{
 PRODUCT_PACKAGES := \
 Calculator \
 Email \
 ImProvider \
 SdkSetup \
 VoiceDialer
}}}

This will include packages in the build which would otherwise be missing (including the SdkSetup package, which will enable incoming calls).

{{{
cd ~/replicant
make
}}}

Wait and wait and wait.

== Flashing the new firmware ==

[to be written]

== Building individual pieces ==

=== Each time you want to build something ===
 * open a new console
 * Then type:
{{{
 cd ~/replicant
 source build/envsetup.sh
 export ANDROID_JAVA_HOME=$JAVA_HOME
 lunch htc_dream-eng
 make
}}}
 * The files to flash are in ~/replicant/out/target/product/dream,flash them and then clear the cache
 * boot and push the wifi firmware if you want it


=== If you want to build a particular project ===
 * open a new console
 * build everything if it was not done before
 * Then type:
{{{
 cd ~/replicant
 source build/envsetup.sh
 export ANDROID_JAVA_HOME=$JAVA_HOME
 lunch htc_dream-eng
 #go into the directory containing an Android.mk
 mm
}}}