In addition to Sasi & Abdul's great suggestions ...
The AIR runtime can directly open local files (which you can not do when targeting the Flash Player runtime, due to FP's security sandbox). You could use your Flex skills + the AIR APIs to open and parse any file. Unfortunately, I know of no published solutions (yet) detailing using Flex in AIR to open Excel files.
Following are various links related to Flex to Excel communication (plus a link related to Abdul's suggestion about using serverside logic to process the Excel file).
Link #1: In browser, targeting Flash Player, using two ActiveX objects embedded in an HTML page. Provides instant as well as on
demand data synchronization between the objects. ActiveX object #1 is the Flash Player itself (with the Flex application executing in it). ActiveX object #2 is a Spreadsheet from Microsoft Office Web Components
(OWC):
Links #2 & #3: In browser, targeting Flash Player, using cut-and-paste from Flex to Excel:
Link #4: Server side using ColdFusion:
Please post back if you develop a solution that you find satisfactory for importing Excel files into Flex (even if targeting AIR).
hth,
g