CPU-Z lists the motherboard as a model "05P36G" motherboard sporting a PM55 chipset.  According to intel's website, that chipset is capable of supporting the CPU I have purchased.  Also, looked up the replacement model number for an XPS 1647 Motherboard.  If there were two motherboards, one capable of only supporting Core i5's and a different one that will support the Core i7, then I should find two different part numbers.  But I can only find one Dell part number for that motherboard which leads me to believe that both the Core i5 and the Core i7 models of XPS 1647 laptops have the same motherboard. 

You're correct that several reported the same problem with retail i7s. It's clear that the mainboard in the systems shipping with i5 CPUs is not the same one that ships in systems with the i7 -- that became apparent since those who tried the upgrade, failed.

I'm sure there is -  you can replace the system board with one from a system that shipped with an i7.   That's going to add over $400 to the cost of your upgrade, though.

For that, you lose your system warranty and get at best a 90-day parts warranty on the system board - or nothing, if you buy on Ebay, etc.

No -- there are other boards:

65C2K --- http://www.parts-people.com/index.php?action=item&id=6666 

Y507R -- http://www.parts-people.com/index.php?action=item&id=6666

The actual distinction between the 1645 and 1647 isn't all that clear - if you look at the Dell outlet, the 45 is the one that lists the i7 and the 47 only shows the i5.

CPU support is not limited to the chipset - the voltage regulators, system BIOS and other components come into play as well.  Given those who've posted that i7s DO NOT work on systems having originally shipped with i5s, it is clear there are mainboard differences and that i5 systems can't be upgraded to i7s.

I'm a tad frustrated.  XPS tech support told me this was possible.  Otherwise I would never have tried.  Everything I can find says I should be able to, yet I can't.  Grrr!!

There has to be a way to do this.  I can purchase a premade 1647 with a core i7.  

Unfortunately, what they might have told you isn't worth much - Dell doesn't support CPU upgrades on any systems.  Neither do any of the other major vendors.

Which is fine, except the CPU I bought based on what they told me was almost $400 and the store policy won't allow a CPU return unless it's defective in which case they only allow for a replacement.  

Presumably you knew that when you purchased the CPU -- so you assumed that risk.

Of course I knew the policy.  Thats why I made a point of talking with XPS tech support BEFORE I ordered the CPU rather than relying on the information I had gathered online.

Then what you didn't know, is the problem - that Dell doesn't officially support upgrading CPUs, on any system. 

I think the i5 mobile processors have an Intel graphics solution in them. I read somewhere that this is done by putting two chips in the same package, one CPU chip (with 2 cores) and one graphics chip. The i7 quad cores are built with two CPU chips and no graphics chip. Maybe your computer does not come up with the i7 qm because it is looking for the graphics chip that is on the i5 processor. You might have better luck putting one of the core i7 dual core cpus (with integrated graphics) in as a replacement for the i5.

The XPS 1647 can come with the either an AMD 4670(older models) or an AMD 5780(newer models) video card,  Neither of those support "hybrid graphics." Beyond that, after looking through my BIOS, I wasn't able to find anywhere to either enable or disable the GPU thats built into the CPU.  It also doesn't show up in the windows device manager.  As near as I can tell, the "integrated" GPU is entirely inactive.  

I have a performance score in Windows 7 of 5.9 with the CPU at 6.8, the RAM at 5.9, the Graphics at 6.7, Gaming Graphics at 6.7, and the Primary Hard Disk at 7.6.  If the integrated GPU on the Core i5 was active, the "graphics" and "gaming graphics" scores would be lower or wildly different.

If it is the onboard GPU that makes the difference, that would be incredibly frustrating because, as near as I can tell, the XPS 1647 does not use it in any way.