The Samurai class remains largely untouched in 3.5, other than a few skill name changes and feat name changes.
I have been converting OA over myself. The weapons are done (and in PDF format), and most of the classes are done as well. The real headache comes in when trying to convert over the Shaman, Shugenja, and other casting class spell lists.
It's easy to go through and change the spells that have only had their names changed in 3.5, it's also fairly easy to delete spells off of the spell lists that no longer exist.....The difficult and subjective part is:
1)Looking at the native OA spells and determining if they 'balance' with the new 3.5 spells.
-and-
2)Looking through all of the new spells in 3.5 and deciding if they should be added to the OA spell lists.
It's the last two that have caused a lot of frustration in trying to convert. Word from Andy Collins over on the WoTC D&D boards a month or so ago was that 'there might be something in the works' by the original author of OA to update it to 3.5, but he had no new information on that, and suggested checking the author's website for any future info.