This is not for the inexperienced. Engadget is reporting that user Narf54321 on the DealDatabase.com forums has done a successful S3 PROM Hack. For the non-geeks, the PROM is the Programmable Read Only Memory chip on the motherboard of the Series3 that contains some of the basic intelligence, including the security that prevents loading modified software on the unit. Late-model Series2 and DirecTiVo units are similarly locked down, and loading hacked software on the units requires modifying the PROM to allow the software to run. This is not for the novice, since it requires de-soldering the chip from the board, extracting the code, editing the hex, burning a new PROM, and then re-soldering the new chip to the board - which is an easy way to fry the board completely.
The DealDatabase.com forums are a hotbed of TiVo hacking - but be warned, they’re not very tolerant of non-technical folks asking questions, it is a fairly hardcore audience. If terms like PROM, gzip, hex editor, and modified kernel go over your head, it is probably best to just read and learn (if you want). They are great forums to learn about hacking TiVo though.
So, what does this mean? Well, it means people are starting to find was to hack the Series3 to load modified software. Right now this is very early, since it was just posted this month, but it is the first step toward having things like TiVoWeb available on the S3 - for those willing to risk the hardware to hack it.