1. You can try this...
Boot into safemod with the key F8 it will lode some files.
After loading the files it will give show you TWO accounts (a) Administration (b) your account. At that same point select Administation account beacuse by default its without password and then login to the windows and change the password of your user account.
2. Visit this like Ophcrack
... download it onto other computer make it bootable with power iso link : PowerISO - Reviews and free PowerISO downloads at Download.com
and boot it, it will give you some easy options through which you can crack the password and use your account.
3. If nothing works then repair or restore your vista with installation disk.
Inform me if you find me helpful.