At this point there are no software programs out there to officially connect a Windows Mobile 5.0 device to OS X. However, not all is lost. Mark/Space has a beta program for those who have Windows Mobile 5.0 devices who want to sync with their Macs. The
Missing Sync 2.5 alpha might do the trick for you. Your O2 XDA Atom is listed under their compatibility list for this alpha version as well.
Check out the FAQ for version 2.5
here. Watch out! It might be a bit buggy, but let us know how it works for you!
-Tim