i installed Ubuntu 12.4 inside my windows 7 in a separate partition named "E" ,but after installation in windows the "E" drive can't see. Where the partition goes? How i can see it through windows 7. And i want to set my default boot os to windows ,which now seems to be Ubuntu.

Most likely a wubi install instead of a Virtual machine.
http://en.wikipedia.org/wiki/Wubi_(installer).

Windows does not see Linux partitions, period. Why would you want it to? You can change your default boot order by using the systems settings for the boot manager, or editing the grub configuration.

I've found the quickest way to get started with Ubuntu in Windows 7 is to first install the free virtual box from Oracle
https://www.virtualbox.org
Then install Ubuntu into the virtual box.
This give a good enough environment for most new users.

Installing "inside windows" is a wubi install where Ubuntu runs as a program inside windows. If you have Ubuntu on a separate partition, that's a different story. Since you are booting with Ubuntu Grub, if you decide to remove Ubuntu or format its partition, you will be unable to boot without restoring the windows bootloader from a windows installation CD/DVD.

To change the default system to boot, edit the /etc/default/grub file using sudo. There should be a line at the top of the file like this:

Count down to the menuentry listing for windows and enter that number in the file above. Count starts at zero, not one.

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i can't edit the grub.cfg file. how can i edit it through terminal. i used "cat grub" to display it. But i can't edit it why? i entered as a root.

The "cat" command is generally used to read a file, not edit it. You need to use a text editor and you should have gedit available to try: