Hi,
Because the function url ('hdr.jpg) takes as the css url
I don't know if that was just a typo in the forum post or it it is a typo in your css, but it is very important to have the url enclosed in single quotes.
url ('hdr.jpg)
needs to be
url ('hdr.jpg')
If it is using http://localhost/ when you think it should be using http://MIOSITO/
then there is something not right about your IIS configuration and/or DNS settings or name resolution.
You could edit the c:\Windows\System32\Drivers\etc\hosts file (first launch notepad as administrator)
and add
127.0.0.1 MIOSITO
Hope it helps,
Joe