Ok, I have Ubuntu installed but I want to install Windows also (dual-boot). Problem is, I don't have a free partition. I have my root partition (15 GB), and my /home partition (300 GB). The home partition has about 50 GB free space, and it's formatted reiserfs. I've heard about tools like resize_reiserfs, and I even tried it yesterday - I shrunk my /home partition (it's on /dev/sda6) with the command:
resize_reiserfs -s -20G /dev/sda6
After that gparted showed that the partition itself was 280 GB, but there was no way to create a new partition from the 20 GB. I ended up running
resize_reiserfs -s +20G /dev/sda6
to restore my /home partition to its previous size.