While installing ubantu I do not remember the password I entered .Hence I am not able to reach my desktop

The only thing you can do is change your password. Probably the easiest way to do this is to boot into single user mode. The last time I checked (edgy), Ubuntu provides an option in the GRUB menu for this called recovery mode. If you do not see the GRUB menu when you boot (and you probably don't), boot the computer and press the escape key immediately after the powerup tests are finished. Assuming you have not created a root password, this will boot you directly into single user mode where you will be given a command prompt. At this point you are running as root. Type passwd followed by the name of the user, press enter, and it will prompt you for the new password twice. You will not see anything as you type the password. After it tells you that you succeeded, press ctrl-D (which either reboots the computer or finishes booting into multi-user (normal) mode -- I forget which).

If all else fails, you can get into single-user mode by appending "single" to the kernel line in the GRUB menu. When the GRUB menu first appears, hit "esc" to stop the count, then "e" for edit.

thanks friends It helped me a lot . I changed my password with the same procdure