threw your motherboards bios which can be accessed at startup
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.
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.
Intel 8088 Intel 8086 Intel 286 Intel 386 Intel 486 Intel Pentium Intel Pentium II Intel Pentium III Intel Pentium IV Intel Itanium Motorola 6800 Zilog Z80
The Intel Pentium Dual-Core is much faster.
Pentium D was the first dual-core cpu.
Yes.
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.