Once you boot to Windows, your computer will find and finish installing the "new" hardware, then likely ask to restart again.... Reverting the Bios setting to IDE should get you back into XP to try again.
This info is important later, and it can be difficult to find out without some annoying trial and error. Hit F2 to access the BIOS, and change the setting on the second page from AHCI to IDE (If you don't have this option, boot back into Vista and update your Bios, downloaded from the link above).
On the Boot tab, change it so your DVD drive is first. Don't worry, we'll switch it back, but it's MUCH more of a PITA to leave it on when we install XP...
My wife recently bought me an Acer Extensa 5620 for Christmas.
It's a great little unit with a lot of potential, but the one big flaw was the operating system: it came with Windows Vista.
I will choose the driver to install." Hit Next again, then select Have Disk.