Can I set the CAN baud rate to 250 Kbps or greater?
No, not with the stock 18.432MHz crystal that comes on the TINI. CAN requires baud rates to be accurate within 0.5%; unfortunately the 18.432MHz frequency of the crystal can't be divided accurately enough to generate a compliant baud rate of 250 Kbps or above. With the current crystal there's no way around this.
You can of course change the crystal if you really need a higher baud rate. To get 500000 bits/s, you'll need to change the crystal to something like 18.5MHz, or you can use an 18MHz crystal and get all the way to 1Mbps CAN rates. This will affect a few other things on the TINI - see http://www.jguru.com/jguru/faq/view.jsp?EID=244466 for more detail.