Pentium

guys pls. help... what are the compatible hardware for pentium III and IV??

What do you have and what are you looking for?
The PIII/PIV era spanned several socket types and quite a few advancments in tech.
What is compatiable with your system really depends on exactly what you have.

Hardware that works with a PIII or P4 would encompass a huge list. However, one thing is pretty much a given- if the parts fit together and your OS has the appropriate drivers, it will probably work. Basically, anything that can fit in a PCI slot or connect to a USB port ought to work just fine if there are drivers. AGP is a little trickier as many of the PIIIs had AGP 2x and the currently-made AGP cards only work with AGP 4x/8x slots due to voltage issues. However, old socket 423 and 478 P4s have AGP 4x or 8x and you shouldn't have AGP issues.

One note about older hardware is that the older hardware generally runs older OSes and sometimes has pretty low memory limits that prevent them from running newer OSes. Very few PIIIs can take more than 1 GB RAM, and many are limited to only 512 MB. The memory limits can preclude you from running newer OSes and newer applications even if you wanted to. Older OSes are often no longer supported by security patches, hardware drivers, or newer programs. You ought not to have to worry with too many P4s as most of them can take 2-4 GB RAM and many are already running Windows XP (and can run Vista if pushed), but many PIIIs at best can run Windows XP and will have a Windows 98, Me, or 2K installation on their hard drive. It is hard to buy a new copy of Windows XP today, so be warned. I do have an old 1 GHz PIII with 256 MB RAM as my file server and it works wonderfully after I popped in a modern PCI gigabit Ethernet card and a PCI SATA disk controller, but I run a text-only (headless, actually) up-to-date Debian Linux installation that only needs 38 MB of RAM to run.