how do I configure hardrive for both mac & pc

One possible solution is to use Disk Utility on the Mac and format the drive as exFAT. However, whether or not it will work depends on the version of the Mac OS you are using (http://www.mactip.net/guide-how-to-format-an-external-drive-to-work-seamlessly-with-macs-and-pcs-without-third-party-software/). Another option is to format the drive as MS-DOS (FAT) from Disk Utility (http://www.wikihow.com/Format-a-Hard-Drive-on-Mac-to-Work-on-Mac-and-PC).
This may also be worth a read: http://osxdaily.com/2012/04/22/format-drive-mac-pc-compatible/