Dual boot (OSX and Linux) from external USB Disk

[QMax]

I hope someone could help me, cause I've not found any tutorial about this.

 

Actually I have on my laptop, WinVista on internal HDD.

I installed successfully Leo Kalyway on an external USB HDD using GUID.

This works fine because my laptop support USB boot, so if I disconnect USB disk i can boot in Vista, connecting USB Disk Darwin boots in Leopard.

What I'd like to do is to create 2 new partitions on USB disk (root and swap) to install Ubuntu or Kubuntu (not sure yet...).

 

My first and only attempt was a REAL DISASTER.

 

Kubuntu killed MBR on both int and ext disk. No more Vista, no more OSX86, no way to boot caused by a Grub error 21... so I reinstalled both OSs from the beginning.

 

My goal is to have a boot choice between Linux and OSX86 only when I boot from USB disk, leaving untouched the internal disk drive containing Vista.

 

Is this possible ?

 

Should I shrink my installed OSX86 (actually I have a single/full size partition for it) to gain space for Linux ?

 

Should I use GUID or I have to reinstall using MBR (brrrr I'm scared...) ?

 

I'm scared because I tried reinstalling kalyway using MBR format and MBR_Bootloader, but this installation ends in a Kernel panic... installed again using GUID and all worked fine.

 

Thank you very much for your help.

 

Max