triple boot Mac, Windows XP, and Ubuntu

I apologize in advance for any lack of clarity -- I have never posted on a forum for technical assistance with a problem, because I usually find the answer from searching. But I have been looking for a good walkthrough / some information about how to triple boot Mac, XP, and Ubuntu (12.10) operating systems on my MacBook.

Here's the "hardware overview" that I found:

Model Name: MacBook Pro
Model Identifier: MacBookPro5,4
Processor Name: Intel Core 2 Duo
Processor Speed: 2.53 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache: 3 MB
Memory: 4 GB
Bus Speed: 1.07 GHz
Boot ROM Version: MBP53.00AC.B03
SMC Version (system): 1.49f2
Serial Number (system): W8930C3C7XJ
Hardware UUID: 2484A489-5F95-5E5B-9E58-08E2A993F5DB
Sudden Motion Sensor:
State: Enabled

I have already installed Windows XP using boot camp, and it's working splendidly. But, I need to know how to also install Ubuntu without causing problems -- which I have read can be an issue because Ubuntu and Windows XP both want control of the MBR (or something like that...)

Can anyone offer some advice or point me to a walkthrough regarding this issue? I'll be bookmarking this thread and checking back soon. Again, I usually don't ask for help on issues like this but I've heard the Ubuntu community is fantastic so I'm giving it a shot!

Thanks!