Mouse not functioning properly in Excel

I have created a spreadsheet in Excel 2007 and then emailed and saved it to a computer that has Excel 2003.  If I use the mouse to select a cell, it highlights that cell and gets stuck into select mode.  Moving the mouse to another cell just highlights everything that I pass over.  I cant get it to un-select that cell.  Cant click on another, right click doesnt work and cant select any other menu on the sheet.  The only way to exit the spreadsheet is by using task manager to shut down excel.  If I use tab and arrows to move around the spreadsheet, I don't have this problem.  It only seems to act up when I use the mouse?  Any suggestions?