Passing userid/password via URL is this insecure?

[jwocky]

Im writing a custom script that needs to pass a user's id and password to another sript outside of vbulletin, I had originally done this via a POST command but for technical reasons I may need to move it to a get method by putting the infomation into the URL (ie http://www.example.com/forum/myscrip...hs78892jsb729d)

My question is, is this a big security risk in anyway? I assume its the user himself that could see the url in the bar so its ok for him to see his own password, and its md5 hash'd anyways so he won't even understand it.

Thanks for any insight into this!