No. The Pentium predates the Pentium D by more than a decade.
There are version of Intel Pentium one through four as well as Intel Pentium Pro, Intel Pentium D, Intel Pentium M, Pentium (2009), and Pentium Duel Core.
Yes. You can upgrade your Dell XPS 400 Intel Pentium D to Intel core i7.
The Intel Pentium D, Core Duos (and Solos), Core 2 Duos (and Quads), Pentium Dual-Cores, and the Core i7.
Celeron doesn't refer to any particular processor series. Celerons were cost-reduced versions of their Pentium equivalents. The Celeron in question could be based on a Pentium 2, Pentium 3, Pentium 4, Pentium D, or Core 2 Duo. In which case the answers would be "Pentium 3, Usually Pentium 3, Celeron, Celeron, and Celeron", respectively.
no
The Pentium D is essentially a rebranded and double-cored version of the Pentium 4. The Core 2 Duo is a much more efficient and powerful processor.
They are the exact same technology, so one is not actually "better" than the other. Intel Pentium Dual-Cores use the same architecture as the Intel Core 2 Duo, just with a smaller L2 cache size. This makes the Dual-Core slightly slower in intensive applications than a Core 2 Duo at the same clock speed. A Pentium Dual-Core will still outperform a Core 2 Duo of a lower clock rate. Pentium D's are older Core 2's renamed to promote newer CPU's.
The Pentium D is basically a dual-cored version of the Pentium 4. It is nowhere near as efficient or powerful as a Core 2 Duo, and it actually generates slightly more heat than a Pentium 4.
Pentium D was the first dual-core cpu.
threw your motherboards bios which can be accessed at startup
It's often difficult to compare the performance of two processors, especially when one is much older. Depending on the type of computations you are doing, you may see anything from no change to a 1700% increase in the Pentium D over the Pentium III.
None. Any processor written for Intel-compatible processors, from MS-DOS to Windows 98 to Windows Vista to Linux to Solaris 10 can be run on a Pentium D.