Select Troubleshoot Program and then, in the new window, select the first entry which is When the wizard has finished you will have two options: Try Recommended Settings and Troubleshoot Program.

Most likely it won't, so you will have to do so manually. This will walk you through a Wizard that will attempt to solve the problem. Right click the one you want to use and select Troubleshoot Compatibility (see Figure 1). Which file you use will depend upon what hardware you are using. Among these files you will see listed entries for both x86 and 64bit. In the resulting window you will see a number of files. Right click the VirtualBox Guest Additions entry (it will probably be labeled as 'D') and select Open. If you click on the Windows 7 Start Menu and then click on Computer you will see that file listed along with Local Disk and Floppy Drive (even if you don't have a floppy drive). The process of installing the Guest Additions will have downloaded a mountable file on your system. The difference is the actual installer won't start up. You will go through the same steps as you would for installing the Guest Additions on Windows XP at this point.

While Vista is running click on the Devices menu and select Install Guest Additions.

The trick for installing Guest Additions in Window 7 is to trick it into thinking it's being installed in Vista.

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