Sometimes it can happen that you forget your password for your Windows Vista account.
First of all, don’t panic, since you will probably be able to reset it, without losing your data.
Just download the following file. It contains a bootable image (.iso) that you need to burn into a new CD. You can use your favourite burning software for this task. If you have no clue about how to burn this .iso file into a new CD, you might want to have a look to the following tutorials.
Once you have the new CD ready for use, you can just boot your machine from the CD you’ve just created. You might need to change your boot sequence from the BIOS for this.
Detailed instructions on how to reset or change your old password (without knowing the original one) are available here.