First thing to know is whether the HD you intend to fit was
originally installed on this hardware ? If so, then you should just be
able to plug in then boot up - the Linux loader should detect the new
OS and add it as dual boot automatically.

If the drive came from different hardware then the loader will still
create a dual-boot but it's a bit of a Turkey Shoot as to whether
Windows will boot up or not.

As for finding information about the hardware, there are tools to do
that and basic info is available in System Monitor or go to Ubuntu
Software Center and search for Sysinfo.

I'm about ready to do a dual boot system myself. I was going to install XP and
then add Ubuntu to it to do the dual system.

Are you saying that I can have XP on another drive all together and Ubuntu will
see that drive and install it in the boot menu? That would be great!

If a HD with a bootable OS is installed into a PC running Linux then
on the next boot it will detect the new OS and add it to the boot
loader automatically.

If that drive is then removed it will still appear in the boot loader
but a simple command run from terminal will remove it :-)

So yes, adding an existing WinXP HD is as easy as that, but bear in
mind what was said about using a WinXP HD that wasn't installed on the
hardware you intend to use it on - you may get lucky but more often
than not you get a failure to boot or a re-activation prompt due to
the change. This may well be accepted on a phone call to MicroSoft but
there's still no guarantee that WinXP will actually work on the new
hardware.

If you want WinXP in Ubuntu on hardware that hasn't had WinXP on it
before then consider Virtual Box as an alternative. Most things work
fine that way and also doesn't mean you have to re-boot to go into
WinXP. VBox allows running WinXP as a program *within* Ubuntu :-)

K> Are you saying that I can have XP on another drive all together and
K> Ubuntu will see that drive and install it in the boot menu?

Without running update-grub?

That's what I've found to be the case when I've done it :-)

Updating Grub is needed to remove the OS if the drive is removed.

try "system settings "....................

Sorry, it's not clear what you want to do. Are you adding a drive which contains
Windows?

To get a full description of your computer hardware, open a Terminal:
cd Desktop
sudo lshw -html >config.htm

When you double-click on the file it should open in your browser, with nice
formatting.