Firewire is a particular type of port an alternative to a USB port. If for example you have an iPod then you would connect that to your PC through this port. Firewire is found to be a lot faster at transfering data than a USB. If you need any more help just contact me.
Agreed with the above except firewire is faster than USB 1.0 but about the same speed as USB 2.0 (which is often advertised on new computers). It is also often used to connect to external devices such as digital cameras, CD burners and hard drives. Since it was developed by MAC, they are more often found on them.
If you need a firewire card for your PC you will find that you can get one for �15/�20 which will just fit into a spare PCI slot in your PC. Your operating system should recognise it OK. Check on the side of the Firewire card box for necessary system reuqirements before you purchase it. I had to get one for my digital camcorder and it works fine.