EDIT: Sorry smith, i'm not trying to be an ass but you could make the argument that he needed the usb driver to copy over TR 1.5 and since you need these drivers to make the S a removable device to copy files to the SD...
A computer is not at all needed to download a ROM. You could
a) Download any 3rd party browser which they all allow the downloading of zip files straight to the SD card (dolphin mini is my new favorite browser) or
b) if you prefer the stock browser, you could download astro file manager (free from the market) and from within astro do Menu > Settings > allow browser downloads and that will allow the stock browser to download zip files to the SD card.
Also, technically, a computer is not needed to root or flash a custom recovery or custom ROM. I rooted a friends optimus S, flashed custom recovery, and he has flashed TR 1.3, 1.4, and 1.5 all without touching a PC.
If a person has chosen to download z4root and root their phone that way, they could then download the files from the recovery thread right to their SD card. Open the zips and place the recovery and flash img right on the root of their SD card and complete the entire recovery process via android terminal emulator (free from the market).
Cheers!