Hi Vasanth,
Approach #1
Use the XML support in Excel to bind your spreadsheet to an XML file with a schema. Then, add logic in your InfoPath form to import the XML by specifying the XSD in the manifest.xsf (this will require manual editing), but it's possible and provides you with a mechanism.
Approach #2
Add the code to access the Web service to Excel and bypass InfoPath. This is probably less work than #1.
Approach #3
Just add the 100 users by hand in the InfoPath form. This is probably less time than both of the above and is less error prone... :)
Good luck
Patrick Halstead [InfoPath MVP]
InfoPathDev
Patrick Halstead
Project Manager at Qdabra