I assume you have Debian GNU/kFreeBSD i386 installed.
If you don't, please refer to the install notes.
Ensure that in your "/etc/apt/sources.list" you have these lines
deb http://ftp.debian.org/debian unstable main
deb-src http://ftp.debian.org/debian unstable main
Create a working dir.
$ mkdir sandbox
Download the sources of the Parted Debian package. From "sandbox"
$ apt-get source parted
This will create a "parted-1.8.8.git.2009.07.19" dir (and others files).
Recursively download all the patches in d-i/people/slackydeb/kfreebsd/d-i/parted/unstable/.
Copy all the patches (without the dir structure) to the "parted-1.8.8.git.2009.07.19" dir.
From "parted-1.8.8.git.2009.07.19"
* apply all the patches
$ for x in *.diff; do patch -p1 < $x; done
* regenerate the "configure" script
$ autoconf
* build the package
$ dpkg-buildpackage -tc
This will create some files; the most important are *.deb.
They are useful to test parted in a normal system, i.e. outside of d-i.
To install them
$ dpkg -i *.deb
WARNING: parted could destroy the content of your disk.
If unsure, please execute parted only in a GNU/kFreeBSD installation on a virtual machine, mounting only virtual hard disks.
Update 20090804:
Update instructions and add warning.