And no, installing a different version of Windows 7
does *not* void the warranty in the US, contrary to our Indian tech (from Dell support, no less...). You lose support for Windows on that machine from the OEM if you didn't use the Dell disc to reinstall (because the OEM supports the Windows 7 install on that machine, and/or any recovery installs from shipped media or a recovery partition only). The
machine itself's warranty is
*not* in any way changed by what OS you run, Windows 7 (either retail or the OEM install from the vendor), as that would violate a few US laws. Reinstalling an OS from anything other than what the vendor ships may void a
service contract, but you would purchase that above and beyond the warranty provided with the hardware at the time of sale - if you didn't specifically add a
service contract for the machine, you don't have to worry about that. You will be fine if you reinstall Windows 7, either from a retail package or from a recovery disc or reinstall disc from the OEM (note, for example, Dell themselves show you how to do this,
HERE). I would expect a Dell tech support person to understand this, at least, but he may not be up on the intricacies of US law with regards to warranties on products sold here - the hardware warranty and the OS support for the software on that machine are two different things, and changing the OS in no way would void the warranty - in fact, even
opening the machine itself with tools to work on/replace "user-serviceable" parts like RAM, hard drive, PCI cards, etc. no longer voids the warranty, although certain portions may be restricted if they are not serviceable.
The only thing to know is that you will need to be aware of who to call for Windows support if you do install Windows 7 again (Microsoft if you reinstall from a retail package, the vendor if you reinstall from recovery/reinstall media shipped with the machine or from a recovery partition preconfigured on the machines), but hardware support will come from the OEM regardless.