Oh, unfortunately the early-intel Macs will finally share the fate of PPC-Macs, when it comes to compatible upgrades for Apps (mainly related to Cloud-accessibility), that need to be revamped very often due to significant changes established by the Cloud-service providers. In the end only the latest versions of any OS are supported and one has to use a Browser to gain access to those Cloud-services.
So that's probably the only solution for You to access OneDrive on Your 2007MB. Find a decent browser.