Login problem in directory instalation

Hi.
I have installed my wordpress 2.5 into a folder inside my domain as the docs says.
Mydomain.com and my wordpress is in Mydomain.com/folder/

I have a problem to login, i need to go to the Mydomain.com/folder/wp-admin/ to login, instead to use the Mydomain.com/wp-admin/ url.
It could not be a big problem, but when i login in the folder url, when i come into de domain.com to make a comment, the form is not filled up auto.

How must i fix this?

Thanks and sorry for the english.