Yes, it is possible to run Linux on it. It's just an ARM system on a chip (otherwise Windows CE .Net wouldn't run). However, how much time are you willing to put into it?
Centrality Communications was bought out by SiRF which was bought out by some hacker-unfriendly scumbags named CSR (Cambridge Silicon Radio).http://www.csr.com/
Here is the Non-Disclosure Agreement you must agree to before you can see any documentation:http://www.csrsupport.com/nda.php
You're not going to be able to agree to that if you are developing open-source code. And it is possible they don't even have documentation for the old Centrality chips anyway.
That leaves reverse engineering of the existing firmware as your only option. This has been done a number of times for various PDA's and mobile phones running windows mobile, so the tools and knowledge are out there. It is just a time-consuming process.