I'm not in the same impression as you for Vista, in some points, I found VISTA has its own advantages.
Since your model was built for VISTA, some of the functions may not work i.e brightness control (Fn +F7 or F8)
However, you are not alone, many CQ40 has downgraded their notebook.
If you wish for XP drivers try the following steps._____
Make your Vista Recovery cd/dvd if you haven't yet, found out here
Your model needs ICH9 sata driver to be sliptreamed in XP CD installer. If you did it right, you'll pass BSOD error.
Use Nlite to sliptream ICH9 sata driver.
A good guide to sliptream sata driver, here
Note: do NOT use sata driver from that guide, your sata driver is ICH9 given below.
ICH9 sata driver,
The driver is located in iaAHCI.inf and is called ICH9M-E/M SATA AHCI Controller, here
Nlite download, here
Some suggestions to avoid problems while installing XP:
1. Try NOT slipstream all of sata drivers, use only ICH9 --> ICH9M-E/M SATA AHCI Controller
2. Use XP-SP2, a lot more easy to use since many of XP drivers were built based on XP-SP2.
3. Burn XP installer slowly and not using the maximum speed, sometimes it create errors
4. Choose a reputable CD media, not the cheap one.
Installing Audio was the most difficult part, since BIOS incompatibility.
Please update your BIOS before installing MS-UAA, at least to F.12, here
F.24 is the latest BIOS up to this date.
Drivers for CQ40-109TU
Intel Chipset,(install and reboot before other drivers), here
Install MS-UAA before Intel graphics (include HDMI sound) and IDT sound drivers , here
Intel Graphic driver, here
IDT High-Definition Audio CODEC Driver, here
High-Definition Audio (HDA) Modem Installer and Driver, here
Broadcom Wireless, here
Realtek RTL8102E Family PCI-E Fast Ethernet NIC, here
JMB38X Card Reader Host Controller Driver, here
ENE CIR Receiver (your Vista driver), here
or if it does not work try Vista driver verified from Intel, here
ALPS Touchpad Driver, here
.Net Framework(required before HP Quick Launch Buttons), here
HP Quick Lauch Buttons, here
If you had Bluetooth, here
If you had for 7 unknown devices (buttons drivers), here
Do manual installation
Go to device manager, right click unknown device,
Choose to update driver, No to connect,
Choose install from a list or specific location, Don't search, Have disk,
Browse to the location of machine.inf.
Do it for the rest of unknown devices
Good luckSource : http://h30434.www3.hp.com/psg/board/message....