Hi, I have installed Ubuntu 8.04 but lost my root password, how can I find it again?

Either that or I will have to reconfigure.

Boot from the installation disc (or use any other live-cd Linux distribution), then mount your on-harddisk Ubuntu's root partition, edit there /etc/shadow and empty root user's password field (first field is username, then comes field separator which is :, then comes password field, then field separator :, ...) Save the file and reboot as you usually would - if you did it right, you should now be able to login as root without a password (because it was set blank).

Mounting a partition (assume first primary harddisk partition to be sda1 and mountpoint /mnt):
Then edit the file:
In the shadow file are stored user/password information, one row per one user. Here's an example of the root user's line (usually first):
First field says "root", second "!" and so on. Second field is the (encrypted) password which you'll want to empty so it becomes like this:
Note that here the password field contained only "!" which is not acceptable char in the password; this means that the account is "locked" and you can't log in as root (default Ubuntu way -- you're supposed to use sudo instead). If you have set up a root password, instead of the exclamation mark the field contains a longish gibberish string which is the encrypted password.

With root account open you can then use passwd to reset other accounts' passwords if you need.

Alternatively you could use single user mode. I believe a quick google seach on "ubuntu single user mode" should give plenty of hits on that. Once in single user mode you can just type "passwd root" and should then be able to reset root's password. Also you may want to check you don't have sudo access with your normal none root account by typing "sudo su -" and retyping your password (not your root password). If that gets you into root then you can just type passwd that way. Single user mode is usually the easiest way to reset a lost root password if their is no sudo access either.

You could, but apparently the latest (8.04) version of Ubuntu has thought about that, and by default will ask a password anyway -- you won't get a free entry to the root account that way anymore

It would be good to go to BIOS settings and (in addition to setting up a password for entering the setup utility) set default boot device to be harddisk, disable boot menu so people couldn't switch to CD and set up a password for altering bootloader configuration/entering single-user mode, but as long as the disk is not encrypted, this is all pretty meaningless -- typically harddisks are fairly easy to remove from the machine and plug onto another machine, on which the disk contents are easy to access (bypassing all bootloader and login troubles).