how to dual boot xp and ubuntu?

Read the Dual-boot tutorial on the Ubuntu website.

Then, watch any one of many "Step by Step" Videos available on the web.

Here's an example:

Best place to start would actually be the Ubuntu forums http://ubuntuforums.org/index.php. The support and answers you'll find there will be able to surpass anything here. Just search there first and i'll bet you find the answers you need... not to mention on the future problems you'll run into getting certain features up and running 100%

That being said, getting an Ubuntu dual boot up and running should be pretty easy if you already have xp on one partition. Download Ubuntu and install it from the disc, make sure when you install it the you don't accidentally erase or install over you xp partition.

You generally need 2 partitions for Linux at the very least - one for the Kernel (think of this as your OS) and then one for whats called you swap file. A lot of folks prefer having a Kernel partition, a Swap partition and a Home partition to keep there documents in... this allows you to update or reinstall linux without loosing all your files.

The installer built into the cd does a pretty good job walking you through the rest. It should automatically install something called "GRUB" which is what allows you to choose what OS to boot (Xp or Linux) when you boot up your computer.

Here are a couple walk throughs

http://ubuntuforums.org/showthread.php?t=675866

http://ubuntuforums.org/showthread.php?t=669364

A good Wiki with explanations and walk through on Dual Boot

https://help.ubuntu.com/community/WindowsDualBoot

I can't stress enough, use the forums... they are such a huge help

Now, I'll assume that Windows is installed on C drive. Then C is your primary partition. DO NOT install Ubuntu here, because that makes the whole exercise pointless.

Make sure you have some space on your hard drive not allocated to any particular partition - this is the portion of your hard drive that is not formatted using NTFS or any other file system.

Now, if you have unallocated space, you can

Boot using the Ubuntu live cd and while installing, allocate this unpartitoned space to the root / partition of your ubuntu installation.

Or, if you don't have space, you can use Partition Magic or any other tool to shrink your one of your existing partitions to create free unallocated space for your Ubuntu installation.

Proceed then with installation.

The grub bootloader that comes with Ubuntu will install itself to the boot sector of your drive and display a boot menu with where you can choose between booting into Ubuntu and Windows.

So, there you have it, your dual-booting Ubuntu/XP system.

Someone else advised installing XP first and then Ubuntu and they are correct. What I would like to suggest to you though, is get another physical hard drive to install Ubuntu on rather than on the same drive. Then both systems will have their native format. Although both systems can exist and operate in the same NTFS file system, if one of them has a unexpected crash it is not uncommon for the master boot record to be corrupted to the point where neither OS will boot. If they are on separate drives, it's a non issue.

Install windows to one of them first

Then put in the Ubuntu CD and install it..

Select the partition your Windows is NOT on, and the other one for the swap File.

Ubuntu will Automatically install GRUB (The menu before the OS loads )

Correct - if you install ubuntu or kubuntu onto your F drive, it will leave your XP partition intact. Ubuntu is Gnome, Kubuntu is KDE (different desktop environments).