Use VMware workstation and point the New Virtual Machine Wizard to a folder on your external USB drive. Install CentOS there. Be sure to select Red Hat Enterprise Linux 4 so the proper drivers will be loaded. This will allow your XP system to stay intact and allow you to run CentOS at the same time. I do this with my Latitude and it still runs quite fast! This doesn't directly solve your problem but is an option.

On 6/24/06, Phil Schaffner <P.R.Schaffner@ieee.org> wrote:

On Sat, 2006-06-24 at 03:01 +0100, Karanbir Singh wrote:
> Mike wrote:
> > Greetings CentOS Fans.
> >
> > I'm working on an Inspiron 9400 Laptop.  It supports booting from USB
> > devices, so I'd like to install CentOS on a USB hard drive as an
> > alternative to XP.
> >
>
> this might not help you, but just so you know - CentOS-4 does not
> support installing to or booting from usb drives. You might still be
> able to do it using some trick or the other, but officially its not
> supported.

Haven't gotten around to trying the CentOS Live CD yet.  Does it support
customization on a USB key (like Knoppix)?

LiveCD+USB key might serve the OP's purpose as an XP alternative.  (Or -
my preference - just shrink the XP partition and dual-boot if that is an
option for you [e.g. not somebody else's laptop].)

Phil