A couple of years ago, I made the vUSB USBaspLoader work on the USBasp. I think that the USBasp is an incredible development target for vUSB:

• it's cheap,
• has a SPI/SSI (and somtimes also UART) pins on a 10 pin header,
• and it comes with a ribbon cable :-)

The USBaspLoader replaces the USBasp firmware. You can, however, program other AVR µCs with it if you flash USBasp through the USBaspLoader onto itself.

The hardest part was that to make the code fit into the 2K boot sector AVR-GCC 3.4.6 was required for compiling the USBaspLoader.

It turned out that for building an old GCC an even older version of GCC is required. In order to get that I needed to bootstrap a historic Linux version, fix a BISON related bug, merge start-up code for other-than-historic AVR µCs, etc, etc. All in all, it imposed a really steep learning curve.

Drop me a note if you're interested in the code, or if you need a patched AVR-GCC 3.4.6 for Linux.