I am looking to upgrade my HP dx2400 desktop from Vista 32 bit to Windows 7 64-bit in order to support a RAM expansion up to 8GB. It appears the hardware is fully compatible with the upgrade, but I cannot for the life of me find a driver download for this upgrade. Does anyone know of a reliable source for one?
Chances are when you install Win 7, it will detect all of your devices and load drivers for you (assuming you are connected to the Internet). Otherwise, all of the drivers you need can be found at HP.com. Remember, you can also use generic sources, like Realtek, Nvidia, AMD/ATI, etc for more current drivers than those offered by OEM vendors (like HP, Dell, etc).
What do you mean you cannot find a driver update? A driver for what exactly are you looking for? Win7 will very likely install and everything will work just fine if you ran the compatibility wizard and it says all is okay for Win 7.
Please note that you cannot do a direct "install upgrade" from a 32 bit OS to a 64 bit OS. (the "upgrade" version of the software that implies the upgrade can be done is referring to the licensing agreement only, that you can buy an "upgrade" version, install it and activate if you have a previous version of Windows installed)
The 64bit version of Windows will save your old Windows installion into a backup folder, and do a complete new fresh install of the 64 bit version. So be sure you backup and save all your data, music, pictures, anything that you do not want to lose somewhere to an external device before you start your upgrade just to be safe.