Crossover confusion: one needs it and two don't

I am mystified by an NIC link and Ethernet cable question. My new Dell Inspiron 530 desktop computer requires a crossover cable where my new Vostro 1400 notebook and my previous computer both require a straight-through Ethernet cable to connect to the same thing.

Here are the configurations that work:

(Old Comp. or Vostro 1400 laptop) NIC jack --- Straight-Through --- Firewall LAN jack

(Inspiron 530 Desktop comp.) NIC jack --- Crossover --- Firewall LAN jack


So the obvious question is: why would one computer (Inspiron 530) require a crossover cable to connect to my firewall while the others do not?