Hi, Saumya.
I haven't seen your data, but the following might get you started on the right track.
Convert your lat/long to decimal degrees.
I don't know if you have any experience with Microsoft Access, but if so, you could consider importing the Excel in Access (very easy), and even consider maintaining it in there, instead of a spreadsheet if you don't need Excel specific functions.
You could than set up a Windows ODBC source / link to the table in Access, that is accessible from within ArcGIS using the "Add OLE DB Connection" option in ArcCatalog. If you subsequently add the table to ArcMap, you can join it to a pre-existing Feature Class, or use X,Y coordinates in the table to dynamically show it as a X,Y point event layer using the tools for that in ArcMap (Make XY Event Layer (Data Management)).
Once setup, any changes made in Access, will be dynamically and automatically reflected in ArcMap (at least each time to you re-open the *.MXD document).
Adding OLE DB connections to databases
Desktop » Mapping » Working with ArcMap » Working with the Catalog window
Good luck,
Joe
