Connecting A Wireless Antenna To A Desktop

At the place I work there is a butler building that has 1 computer in it. It is too far away to connect to our network with CAT5 so I was thinking about connecting a wireless antenna directly to the computer so it can connect with our network. What do I need to connect the antenna to the computer directly?

Depends.
there are wireless pci cards you could use.
or there are usb wireless adapters.

Also, if your network does not already have a wireless routuer, youd need one of those.
And make sure the computer is within range of the router.

1) Wireless Router (B/G are most common, G being better overall).
2) Network adapter, they come in PCMCIA, USB2, PCI, USB1.1, Integrated...

Check that your computer [laptop] doesn't have a integrated adapter first.