ok it's not too painful really. First of all you will need to install a tftp server on your PC. Solarwinds do a free and safe one.
http://www.solarwinds.com/products/f...tp_server.aspx
Once you have installed it and started the tftp service just copy the firmware binary file into the tftp root directory and point your router at your computer* at the firmware update page.
*You might have to reference your computer by it's IP address