If you just want to try out ubuntu you do not need to install it on your hard drive. Actually if you do not want to back stuff up then you probebly should not install. Its not that its hard to remove ubuntu once installed, (its actully easy) but that in order to use it in a dual boot senario you must resize your partitions. This in itself is risky. If something goes wrong you can lose all your data.
The live CD is slower but works great. The one problem is when run from the live CD it will not automaticly mount your normal hard drives. This will make it a little more confusing for you, especially if you are not used to linux. Anything you use in windows can be used in ubuntu. There is one other problem with the Live CD, you will not be able to install programs, it will take up a lot of memory. This includes some multimedia programs and plugins (including the ones to play certin media files).
Personally I am using a laptop with Ubuntu on it and Windows. It works great and I did not have trouble with the resizing. (but i was also lucky because i did not make backups).
To get your XP partition mounted in the live CD, try this.
1. On the Applications menu and under accesories click console.
2. Type the following (I am assuming you have standered IDE drives and that your windows is on the first one):
sudo mkdir /media/hda1
sudo mount /dev/hda1 /media/hda1
exit
3. Use the file browser to acsess your hard dirve, It should be in the folder media under hda1.
This is not needed once Ubuntu is installed, it should set up automaticly.
REMOVED
REVISION:
I just found this. It is designed to avoid repartitioning and installing a boot loader. I have not tried this yet (but I will) and it is still a beta but you may want to look at this. http://cutlersoftware.com/ubuntusetup/
I have also removed how to do stuff with the MBR. Not only was I going past the original question I also had something wrong that could crash a computer bad. I will assume it is not needed right now.