Ext4 got some attention recently because it was able to boot ubuntu to the login screen in about 20 seconds. However, the current daily release doesn't support installing with Ext4. Here are the instructions for installing Ext4 onto the Ubuntu 9.04 (Jaunty Jackalope) daily-live cd.
First of all. Back up all your data. Don't do this on your primary computer. This is still ALPHA software. If you have an existing Windows or Linux install, you'll have to do partitioning differently. If you don't know how to do that, this guide probably isn't for you.
Now then, the guide:
1) Download the 9.04 daily live from here:
2) Burn or mount in a VM
4) Run the installer. When it asks for partitioning, select manual.
5) Create a small (128m is good) Ext2 primary partition and mount it at /boot
6) Create a swap primary partition (1024m is a good min, up to however much ram you have is good. No more than 4096m is necessary).
7) Create a third primary partition that uses the rest of the space, type Ext3, mount as root.
8) Proceed through the rest of the install.
9) When it asks you if you want to reboot, say "Continue using livecd"
10) Open a terminal
11) Your root partition should be /dev/sda3 if you just had those three partitions. If not, substitude /dev/sdaX for /dev/DEV when I mention it.
12) On the terminal, run "sudo tune2fs -O extents,uninit_bg,dir_index /dev/DEV"
13) Then run:
sudo fsck -pf /dev/DEV sudo mkdir /mnt/root sudo mount /dev/DEV /mnt/root sudo nano -w /mnt/root/etc/fstab
and change the "ext3" to "ext4" on the / partition.