You can't run them at the same time if that's what you're thinking of (well, actually you can run one inside the other as a virtual machine if you get some special software but that's probably not what you were thinking of).
You can install them so that you can select which you want when booting, but it's a bit tricky.
Personally I've never tried it, but searching the web for "dualboot linux xp" should give plenty of starting points.
Also look for specific info on installing and running linux on your laptop. They are finnicky machines and quite often there's problems that need some lowlevel tweaking to resolve.
You are looking at a re-partition, and a re-building of your XP environment to make room for Linux, unless you run it under some VM operation. Make a backup first, then partition your drive, and then install XP, and then install Linux. Detailed instructions are all over the place.
Unless you're the kind of person that enjoys partitioning and installing operating systems, or you REALLY have to have a Linux partition, get a live CD such as Knoppix or Mandrake Move. It's so much easier.
I've done this in the past. Not on a laptop but on a desktop that was running windows XP. I used Partition Magic 8.01, really any version. But I first resized the partition, made it smaller for XP, still leave some space for downloads.
In my case I had a 20gb hard drive. I resized it to 10 and 10 or whatever the exact was. Then restart and I had 2 drives. Then download whatever distribution of linux you want: http://www.linuxiso.org/ . Or if you have your own cd already, make sure the bios is set to boot from cd, restart. Go into the installation, it will prompt you where you want to install linux, choose the new drive. Done.
I have did this with Mandrake 10.0, Fedora Project - Fedora Core 2. They both prompt you and have great GUI (Graphical User Interface)
Next one I'm going with, on seperate machine, solely for linux is either Debian, or FreeBSD.
I have not done it before while windows is still loaded.
Easiest way is to repartition the drive.
back up anything you want to back up on your current windows.
Partition the drive as normal only in two sections.
Then load the operating systems.
However, make sure you load windows xp first. If you load linux then winxp then winxp will overwrite the linux boot loader with its own and you won't be able to select linux when you go to select which operating system you want to run.