There is no risk of XP being messed up by Linux because
(1) You cannot but install them in separate partitions. To put a LInux inside XP you need a very special distro and Ubnuntu is not one of them.
(2) XP and all MS systems do not support Linux and so none of them would mount a Linux partition for you to work across two systems. So no damage possible from the XP side.
(3) Linux currently refrains from writing on a NTFS partition that XP uses. It can read it only but can read/write all the other MS partition types. Theoretically you can't use a Linux to damage a XP system.
Most of the problems is to do with booting because we learn nothing in booting with MS systems. However Linux has super ability in booting several systems and simple steps are available to solve any booting booting problem,. especially with the help from the forum.
Since you have a Live CD from Unbuntu you can load it up to see if everything works first. The Unbuntu Live CD is not installable and you need to run the other CD if you start the installation.
20Gb is ample. You need two partitions. One 10Gb large for Ubuntu and 1Gb for Swap, which is a scratch working area. You should partition the hard disk using the Live CD. The best way, in my opinion, in to use the command prompt by clicking system, then terminal.
Ubuntu operates a security system whereby the commands affecting the system are privileged and require "sudo" added to the front in order to invoke the admin rights.
Therefore if you want to see the partition of your hard disk the standard command is
To partition your hard disk hda you use
Code:
sudo cfdisk /dev/hda
You can try the partition program "cfdisk" on device "hda". Nothing will be implemented until you click "write". You will see Linux automatically assign partition ID "83" for its own occupation and partition ID 82 is reserved for Swap. XP partition will have ID 7. Fat32 will have ID b. These are extra things you need to learn because you are using 2 systems.
Have an exploration first and let us know if you are ready to start.
In Ubuntu you can see your XP partition as follow ( I assume you have a IDE disk and known as hda in Linux. As a rule XP will grab the first primary partition known as hda1. If you use a Sata hard drive it will show up as sda). You basically "make" a temporary directory in Linux's /mnt directory, "mount" the device partition hda1 on it. Thereafter you can goto the graphic desktop to see the photos, play MP3 music stored in the XP with Ubuntu. The commands to make the directory and mount it are
Code:
mkdir /mnt/hda1
mount /dev/hda1 /mnt/hda2
When you log off the XP partition will be automatically dismounted. You will see everything in the XP partition can be read but not witten. To transfer data between the 2 systems to need a "neutral partition" in Fat32 that both XP and Linux can read and write.
Thus it may be a good idea to use the balance of the 20Gb for making a data partition in FAT32.
Lastly a hard disk can have a maximum of 4 primary partitions. According to your information you can have
hda1 as the existing XP partition type 7
hda2 as the new Linux partition type 83 for Ubuntu
hda3 as the new Swap type 82 and
hda4 as a new data partition in Fat32 type b
All as primaries. If you have other existing partitions then the last 3 can reside in logical partitions.
In a hard disk one primary must be given up to form an extended partition inside which a maximum of 59 logical partitions may be created for an IDE disk. A Sata disk can have a maximum of 11 logical partitions. Users normally use up the space before the maximum number of partitions is reached.