Or would I need to upgrade to XOOPS 2.0.7.3 to upgrade the newBB from 1.0 to 2.0rc2??

2.0.7.x will be needed for the latest version of newbb to work properly. I do not think it has been tested on earlier version as many bug fixes and patches have been release over the past year.

There have not been any new tables addd into the XOOPS DB, so an upgrade will for the most part be painless. You will of course have to be carefull of other modules that may or may not upgrade along with your XOOPS core.

Theoretically, it might work, but you may have to test the upgrade yourself to be sure. I'm sure one of the developers will know for sure on what steps to take.

I'd recommend upgrading XOOPS to 2.0.7.3 first. I doubt if the newBB upgrade scripts have been tested a lot on old versions of Xoops.

In any case, remember to do a full backup (database + files) first, so that you can revert back if needed.