There's a girl in one of my classes that I like, I found out she had a boyfriend though. I then found out that she broke up with him about a week ago. Should I wait a bit, or is it OK to ask her out now?
There is NO way someone is ready to be in another relationship 5 days after a breakup. This comes across as really selfish and inconsiderate. All you are thinking about is what you want, which is to be with her right now. Take into consideration what she must feel and what she needs, which is space and time to deal. Don't complicate her life or yours by not giving her that, it's just not fair. Be a friend to her, be there for her. That will build a strong bond if you really care about her.
Obviously if she was with some guy for 10 years and is really upset, then wait. But if she was only with the other guy a few months, just go for it.
If there is a girl you like, and she is single, it is almost ALWAYS a bad idea to procrastinate. Just man up and take your shot. if you put it off for one week, you might then put it off for 2, then a month. Before you know it a year has gone by and you never made a move.