Note that this is a possibility only as I have no experience with what I am about to suggest
As you discovered Canon's Image Transfer Utility is only supported in Windows 7. However there seems to be technology included in Windows XP that could allow for the functionality that you are looking for.
From googling some random terms about image transfer from cameras to Windows XP, I discovered Picture Transfer Protocol
Picture Transfer Protocol (PTP) is a protocol developed by the
International Imaging Industry Association to allow the transfer of
images from digital cameras to computers and other peripheral devices
without the need of additional device drivers. The protocol has been
standardized as ISO 15740.
From that same link:
A number of protocols have been developed that extend PTP. PTP/IP,
developed by FotoNation and first implemented in a round of Wi-Fi
digital cameras by Nikon, Canon, and Eastman Kodak, allows data
transfer over any IP-based network.
And that sounded promising, but the article also had a link to Windows Image Acquisition that was first included in Windows ME.
Windows Image Acquisition (WIA; sometimes also called Windows Imaging
Architecture) is a proprietary Microsoft driver model and application
programming interface (API) for Microsoft Windows Me and later Windows
operating systems that enables graphics software to communicate with
imaging hardware such as scanners, digital cameras, and digital video
equipment. It was first introduced in 2000 as part of Windows Me, and
continues to be the standard imaging device and API model through
successive Windows versions. It is implemented as an on-demand service
in Windows XP and later Windows operating systems.2
This inspired me to search for WIA drivers for XP, and then I hit pay dirt! An article from Canon themselves: How to install the WIA driver for my camera
WIA stands for Windows Imaging Acquisition. The Windows Imaging
Acquisition package is an integral part of Windows Me and Windows XP
(the WIA features are not available in Windows 98 or Windows 2000).
Using a WIA Driver (similar in function to the Twain Driver) with
Windows Me or Windows XP provides two advantages: (1) when you connect
your camera to the computer, it will give you the option of download
pictures using the Windows Scanners and Cameras Wizard, which will
start automatically in Windows Me, and (2) your camera will show up in
Windows Explorer as another storage device on the "tree" on the left
side of the screen. It will show a camera icon and will be displayed
below your hard drive and CDROM drive. As such, you will be able to
see a list of the image files stored in your camera, and you may
transfer them out as you would from any drive.
This seems to be exactly the functionality that you are looking for. However as previously stated I have no idea if this will actually work, and how you get the drivers onto your XP box etc.