Where to start on this one. It is always nice to hear about someone considering the switch to the Mac OS but I have to ask, what prompted your train of thought and how much research did you do? The Mac OS will NOT run on your Dell Inspiron 5100 machine. In fact, the Mac OS will not run on any machine that runs windows. (with some exceptions).
The Mac OS runs only on machines built by Apple which is one of the reasons why the system is so stable, secure and a pleasure to use. The hardware is designed to take full advantage of the OS and the OS, also built by Apple, is designed to take full advantage of the hardware.
Your best bet would be to start with the Mac Mini, you will need a USB keyboard and mouse and a monitor. The Mac Mailorder houses are adding a KB and Mouse with the purchase of a Mac Mini.
I am considering switching from windows xp to a mac os on a dell inspiron 5100 with a pentium 4 processor (not sure what other info would pertain to the answer).Is this possible or is a mac pc required?
What other requirements do I consider?