Yes, you can dual boot Linux. It is very easy and you don't need to buy any additional software, Linux distributions already come with everything you need to set up a dual boot computer.
I'm currently dual booting Windows XP and Xandros Linux 4.0. Before I got Xandros I was dual booting Windows XP and SuSe Linux 10.1.
I will walk you through the steps to dual boot your Windows XP system.
1. Windows must be installed on your hard drive first before you install another OS. This is because Windows will only take over the entire hard drive.
2. Disable Windows Virtual Memory.
3. Defrag your hard drive.
4. Put the Linux boot CD in your ROM drive.
5. Restart your computer.
6. Linux will analyze your system and suggest the number of partitions and partition sizes. Some like SuSe will suggest a Windows partition, a root partition, and a user or home partition. Others like Xandros will just create a Windows and a Linux partition.
7. Accept suggested partitions. Believe it or not Linux really does know best.
8. Finish installation and reboot.
9. After your PC goes through post you will see a screen that ask you what OS you would like to boot.
10. Use the arrows to select Linux or Windows. If you do not choose an OS after a few seconds you will automatically boot into Linux by default.
While it is true some installations of Linux are extremely hard to do, other distributions are as easy as selecting left or right handed mouse, keyboard layout, setting date and time and checking for updates.
SuSe took me a couple of hours to install. While Xandros was about 4 mouse clicks and a total of maybe 20 minutes.
The most recommended distributions for people migrating from Windows are:
Ubuntu: uses the Gnome desktop enviroment, is free to download, updates frequently, and is based on the very stable Debian Linux.
http://www.ubuntu.com
Kubuntu: same as above except it uses the KDE desktop enviroment.
http://www.kubuntu.com
Xandros: uses KDE, is based on Debian Linux, cost about $60 and comes with a users guide and stickers to place on your PC. The home Primium edition is packed with proprietary features and a security suite.
http://www.xandros.com
Mandriva: uses KDE, is based on Red Hat Linux, comes with Cedega (allows you to play Windows games), Kapersky Anti-Virus, and LinDVD (the only legal Linux DVD player), it comes in a Linux for beginners package with a manual for people new to Linux and a Linux poweruser package with a manual for advanced users. Figure spending about $40 for the beginner package, and between $70 - $90 for the powerpack.
http://www.mandriva.com
Linspire: uses KDE, has lots of free and commercial software. It is designed to look as much like Windows as possible. It was originally called Lindows until Windows sued them.
http://www.linspire.com
The KDE desktop is a Windows like enviroment. The Gnome enviroment is something different and is prefered by many advanced Linux users.
If you want to know more about Linux distributions go to http://www.distrowatch.com
If you have any other questions feel free to e-mail me and if I don't know something I can at least point you in the right direction.