This is very easy to do. For example in PHP:
$to = "firstname.lastname@example.org";
$subj = "Spoofed mail from Jer";
$body = "Hello there";
$headers = "From: Jer <email@example.com>";
$sendmail_params = "-firstname.lastname@example.org";
I use this all the time for sending email from automated systems on SuperJer.com, ClassifiedAds.com and other sites.
But if hotmail is using SPF, and your email server or client bothers to check SPF records, the email should get marked as spam or dropped completely.
SPF ensures that only authorized IP addresses can send mail on behalf of a particular domain, but only if your email system checks the records.