AFAIK an officialversion hasn't been written for Vista as yet, so you may be better searching for a website to do it for you.
Orin the meantimethere is a workaround:
Here's a useful workaround. When you email pictures, you have the option to resize them before sending. So from Explorer, right click on the image and chose "Send To->Mail Recipient." Choose the size you want. If this is your first time using mail, you'll be asked to provide email settings. If you won't be using email, you can just specify a few random characters in each field. A email will be generated that contains your resized image(s) as attachments. You can drag them from the email and do with them as you wish. Then close the email without sending.
