If you share your computer with other users it's fairly simple to regain access to your account. You could ask one of the other users to log on to Windows with their password and perform the following steps :
Click the Start button
In the "Open" field, type "control userpasswords2" (without the quotes)
Windows opens a user accounts dialog. Select the user with the lost password and click the "Reset Password" button. Enter a new password (and a second time in the confirmation box) and click ok. Click ok once again and you are ready.