Doing this in a simple way has eluded me for a long time. I have described previously here and on my blog various options for importing from Word tables and Excel pivot tables, but have never worked out a simple way to import tasks, especially multiple tasks, with task data such as due and start dates, priority, percentage complete etc.
I now think I have found a relatively simple way to do this. I'll describe it in more detail on my blog when I've had time to develop it more but I thought I'd describe it now as a work in progress to get some feedback.
Essentially it involves importing a dummy task from MM to Word to ensure that you have the MM topic styles in your Word template and also to see how the task information is laid out, which is in a table with a specific structure with quite specific formatting for each field, especially in relation to the start and due date fields.
Then you construct a more streamlined user-friendly of the table with each column formatted in the same way and with the appropriate MM style applied. Unfortunately there doesn't seem to be any way around having to split the table so that each row is in effect a separate table (with the topic notes if there are any appearing in a non-table format below each task). However once you do this the tasks are imported to MM without any dramas.
While there doesn't appear to be any way to import tasks easily directly from Excel you can do so via Word using this method, which means that you can use Excel's features to generate a range of dated tasks for example (which is the reason I started looking at this). As I said I'd welcome feedback and will post more on this approach in future.