I recently purchased a Mega 2560 board and I'm currently attempting to install. I believe that the com port and drivers installed correctly, because when I enter the application one of the menu items under Tools > Serial Port > is COM4, which didn't previously exist before I began installation. My problem is that I can't upload a program, because when this is attempted, I receive a message that 'No board selected; please choose a board from the Tools menu'. However, no boards appear in the list when I navigate to Tools > Board. I downloaded the software and placed it in a Directory called C: \Arduino. Any assistance with this will be appreciated. BTW, I'm installing it on a MS PC running XP.
You may want to try deleting the current files and trying something like below.
Down loaded the below file, make a folder called arduino and put the zip file in it. Unzipped the file using winzip and it made the appropriate sub folders in the folder I made. In the folder I made there is an arduino-1.0 folder, in which is arduino.exe. Double click on the arduino.exe and the IDE should start. See if the board selections now appear.