Falsifying the senders email address

How easy is it to send an email, only to falsify who the actual sender is? Just after checking my Hotmail, and I got an email purportedly from my email to my email with this lovely photo and a link.
http://www.viagra.com/PublicResource...ets/1.0_p1.jpg

Obviously its junk, and as I'm still under 40 I clearly didn't email this to the same account. Is my hotmail likely to be hacked/some virus on it or can crooks easily send out emails and fake who the actual sender is?

No, your email address is just on a spammer's list. They send it to and from the same address to try to avoid junk filters.