Do you have a Tools->Data Connection Retrieve data SharePoint List set up?
Is it pulling all of the data into your form? If so, you just need to filter correctly using the right rules. Cascading dropdowns and repeating tables need preceding-sibling xpath functionality to work correctly. Check out Greg Collins blog on setting the axis correctly - that may be related.
If you aren't gettting the data into the form, it's likely a SharePoint default view problem. Check to make sure all records show up when you navigate to the SharePoint list. If not, you'll need to unrestrict the view to show all records.
If you have >1000 list items in your view, performance will suffer and you may need to put a Web Service on the ShP box to filter in a performant way. We provide a free trial of our WSSP service that does this.
Hope these ideas help!