Here is one link from a site I use all of the time.  Good luck in your quest.

http://windowssecrets.com/2008/02/14/01-Make-your-computer-dual-boot-Vista-and-XP

Charles you may also want to take another approach. Older Windows OS's have to be installed prior to new(er) ones. It can be painful. I highly recommend System Commander by VCom (now Avanquest) LINK. You can add OS's in any order or type (Linux, Unix, OS 2, etc.) and remove them if needed. It also comes with some nice partitioning tools (resize on the fly, hide, copy into another). I've used the program since 1998, including the latest edition and I've never been disappointed. It's a bit pricey (look for coupons) but if you think you might want to make adjustments after your install(s), I think it's worth it. I know the hard core will say Bah, but if you need it done right the first time or you regularly fiddle with new or old OS/s check it out.

i will try to explain my way with a short text.

You have to now how to start a computer from CD and u have to know how u install windows xp. For way one, u also have to know how to burn isoimages. And of course: you have to know how to find things in google

If u only have one partition you have to divide your partition first in two partitions.

Way one: get a geparted cdimage and use this program to devide your partition. if u dont get a screen at bootup try the "force Vesa" option from the bootmenu.

geparted:

http://www.mikestar.com/Record/play;jsessionid=E6D28B38EA1D24D2DF3B8F4435AB1BF9?record=dZW6dG79jo25H

way two: u can use the vistabuildin partitioner. As i dont now the english names for the menus, i cant say were u found it in our version, but i think its controlpanel > administration > computeradministration > volumeadministration... there you can rightclick your partition to shrink it. But it often doesnt work.

next step:

Start your laptop from the windows xp cd. create a new partition and install winxp on this partitione (the second).

After that u have windows xp on your drive but vista doesnt start anymore.

Now u have to start your computer with the vistaDVD an click on repairoptions and that "fix startproblems" (as u now.. maybe this option has another name ).

After restart there must be an bootmenu with vista and xp. If it isnt use the program easyBCD to rebuild the bootmenu.

EasyBCD:

http://neosmart.net/dl.php?id=1http://neosmart.net/dl.php?id=1

If it still doesnt boot u have to use teh commandoline utility from teh vistaDVD. U will find a howto with google

i hope it works for u, but of course, i dont take any warrenty

hope my text is understandable