Can I export a Zoho project in a format in which it can be imported into MS project or Open Project?

Viv,

No. You can export tasks & milestones in either .xls or .csv format.

We are planning to provide project data export in XML format. 

In addition, a format compliant for importing into MS Project will be analyzed and if feasible, might be provided in future.

Is it possible to update the existing Zoho project by "merging" the same MPP file again? After my initial import, I cant seem to update the project via uploading the MPP file again without creating duplicate entries.  On a related note - is it possible to delete ALL tasks in a single go rather than having to delete the individual parent nodes?

@iamasuperuser,

No, it's not possible to update the existing project by "merging" the same MPP file. As of now, if you import the same MPP file again, all the data will be duplicated.

It's not possible to delete ALL tasks in a single go, unless you delete the entire project. 

If I have an xml file, coming from JIRA, how can I convert to this obscure MPP format?!  And why on earth is MPP the standard format for importing?

zoho project is a good software to use but you can also consider several other project management softwarethat you can try out like the 43 alternative that my link includes.