Most people ask this in the context of having just had unsafe sex. They often miss the point that there ARE actually diseases other than AIDS - many of them far more likely to infect and harm you during unsafe sex. AIDS is actually not that good at getting transmitted. For instance, if you get pricked with a needle previously used on someone with HIV, you have only a 0.3% chance of getting infected. Far more serious is something like Hepatitis B: in first world countries it's much more common, and kills more people. And it's transmission rate in the above situation is around 30% (you are 100 times more likely to be infected with Hep. B from a needlestick injury).
I don't mean to underrate the disease - where I come from, the disease is the #1 health problem. Rather, I mean to impress upon everyone the notion that safe sex is incredibly important. Just because you can't get HIV from doing [whatever] doesn't mean you should now throw caution to the wind!
Anyway, enough preaching. An EXCELLENT site that will answer virtually any question starting with the words, "Can I get HIV/AIDS from ..." is here: http://www.avert.org/faq1.htm#q1
I've read the page and can confirm its accuracy; there are further pages dealling with other aspects of HIV/AIDS too. Check it out if you're interested. It's really comprehensive, and I gladly hand you over to them. Feel free to leave me a question if there're still outstanding issues.
Hope that helps!