The simplest way to do it is through Excel and the method works for accessing things like Sage as well.
What you need to do is to create an Excel Spreadsheet and use the Data - Import External Data - Import Data option to get data from Access. The wizard will talk you through which tables and fields you want to import. Then, you save the Excel Spreadsheet off as a CSV file and import it into Progress.
This sounds very clunky, but what you can do is to save the SQL query generated by the Wizard as a text file. Then you can create a number of SQL Templates to query different tables. Once you've done that, you can set up a spreadsheet with an _auto_start macro so that the spreadsheet performs an SQL query from a set text file, imports the data then saves it off as a set CSV file. Then to run the query, you copy whichever SQL template you want to the set text file, open up the Excel Spreadsheet, let it do its business and close down, then copy the generated CSV file into another location for processing.
Once written, it is a lot easier than it sounds.
I've used it to get information from Sage Invoices, Products, Orders, Stock and to generate EDIs form Sage. I've also used it to take information from a bespoke Access database.
If you need code samples, let me know and I'll try to dig out some examples.