http://wiki.maemo.org/Documentation/...l_Installation
Install the SDK, download the source inside the scratchbox ~
cd into the directory, run ./configure, then make.
You'll have to install and/or compile missing dependencies.
The SDK download is 2,475 items, totalling 772.9 MB (including the nokia-binaries)
The install unpacks to about 2GB as far as I know.
You need to have linux installed on your PC.