Buy a USB programmer - any USB programmer needs a processor on board, which itself needs programming - so you need to either buy one ready built, or buy a pre-programmer processor from somewhere.
You can do it *WITHOUT* another processor if you can switch to AT89S2051 instead. I am currently working on it, but the idea is to use a usb to serial cable, then, use some vicious bit banging techniques to simulate SPI protocol...
Some sites outhere allready made it, but only for AVRs.. i'am trying to do it for 89Sxx microcontrollers..
You can do it *WITHOUT* another processor if you can switch to AT89S2051 instead. I am currently working on it, but the idea is to use a usb to serial cable, then, use some vicious bit banging techniques to simulate SPI protocol...