If you want to have great results as Spudman says you would have to pass through an interface and you can use for example T Bone SCT 2000 microphone which is a very nice and affordable microphone
http://www.thomann.de/gb/the_tbone_sct2000popkiller.htm

If your budget is very limited you can directly buy a USB microphone
http://www.samsontech.com/products/p...fm?prodID=1810

I think teh sennheiser is also good (sorry i only found it in french)
http://www.conrad.fr/micro_usb_postc...0_18834_535731

Jipes