what is the difference between Pentium Pro with 256 MB and 64-bit Intel/AMD with 512 RAM when it comes to the recommended hardware specifications for RHEL 4

have you tried googling the hardware and doing your own research

also RHEL 4 is End of life for support level3

Install the current RHEL 6.2

why is it impossible to install rhel 6.2 on an hp laptop.what do i need to have.

from the red hat web site did you notice that under "products" is listed
Desktop
Server

Red Hat Enterprise Linux
is mostly a server Operating System .It mostly works on most laptops but is intended for a rack mounted server

so installing it on a laptop is a "crap-shoot" , it might fully work,it might mostly work or it might not even install .
https://hardware.redhat.com/

Also RHEL is not free .You MUST buy a support contract .
it you ARE going to use rhel you need to pay for it

also what is the hardware specifications on this "hp laptop"
Have you asked the reg hat support people if your laptop is compatible


https://access.redhat.com/support/contact/

Yes, while it's not totally unheard of to install RHEL on a laptop, that's not what it is targeted toward. There are many other GNU/Linux distros which satisfy that need better. If you can't pick one, then try Ubuntu.