You will at least need a new motherboard. The rest of the hardware in the Pentium II is probably so old that I would buy a new computer instead which has all new hardware.
That would require purchasing a new motherboard, processor, and power supply.
The Intel Pentium 4 3.0 GHz processor is a single core processor, but if you'd like to upgrade to dual core, have a look at the Intel Pentium 4 531 3.0GHz Processor Upgrade RH008AV.
There is probably no need to reinstall Windows after a processor upgrade, and the performance increase between the two said processors is probably not worth purchasing a newer version of Windows for.
having high speed.
Neither. It is a computer processor.
Pentium 4 sockets were sockets numbers Socket 423 for early Pentium 4's. Then socket 478 for Pentium 4, Pentium 4 Extreme Edition and Celeron and socket T (LGA 775) for Pentium 4, Pentium D dual core, Celeron D and Pentium Extreme Edition.
The Pentium 4 and Pentium 4 HT differ only in the "HT" designation, which means "Hyper-Threading". Hyper-Threading allows one physical processor to represent itself as two "logical" processors to the computer, doubling the amount of tasks the computer can work on. It effectively allows you to have a dual-core processor while only paying for a single-core. Get the Pentium 4 HT!
No! The older parts from the 486 would slow down the Pentium.
No, it will not. Pentium 2 fits two sockets (with adapter for one of them) 350 and 370. When Pentium 4 fits three different sockets 423, 478, and 775.
There is no Pentium 5 processor. The mainstream (non-budget) Pentium line ends with the Pentium D, which is essentially a dual-core Pentium 4. The Core Solo, Core Duo, Core 2 Duo, and Core 2 Quad all have a very different architecture from the Pentium 4.
Yes.
It has 4 ALU units. A Pentium 4 has 2 ALU units. The Pentium D is like 2 P4's....sooo..... 2 cores x 2 ALU's each = 4