I'm an undergraduate student of computer engineer, and would like to spend the first semester of 2013 working for a startup in the US.
What kind of Visa do I need to get? Do I need a job offer prior to going and look for a job? And, what skills do I have to have?
You can pay for the expenses but you still need a sponsor. It's kind of weird. You have to pass an interview with the sponsor and then they review your case and give you the files you need to get for the visa at the US embassy.
for the skills it depends what you're looking for.