A Pentium 4 will have PCI, so basically any new internal card should work. An external USB card may work, but I can't say for sure if you have USB1.1 or USB2.0. It won't really matter besides performace, but regardless, I'd advise getting an internal PCI card.
I don't understand your question(and please use the edit function in the future) but you're not limited by much of anything...