I will try to give you what advice I can. To give you context of where I am coming from, here is my quick bio: B.S. with ten years in the analytical chemistry industry and now I am a first year student in a full-time MBA program. So I am a technical person with around zero knowledge of academic and formal business topics prior to enrolling in my MBA program. Furthermore if you asked me six months ago I would not have called myself an entrepreneurial minded person. However now I am on a leadership team with other students starting an entrepreneurial club encompassing all academic departments (we have law students, medical, engineer, business, undergrads, and the art institute nearby).
First off, I do not think there is really any one class you could ever take so as to learn "entrepreneurial stuff." Personally I think if you want enough knowledge to be able to improve your chances of having a reasonably successful business you essentially should get a MBA. However I also think people who go get a MBA immediately after undergrad are doing themselves a great disservice. As an aside our university has a Masters in Engineering Management program that partners between the business and engineering schools - may be worthwhile to see if your university has something along those lines.
Anyhow, I say that you essentially need - or rather ideally the skills you want - may be found in a MBA program because you really should study various fields. I can see how marketing can be extremely valuable for an entrepreneurial type person. Somebody mentioned accounting, and being able to structure how you will do costs could literally make or break a start-up. Same thing with finance, if you sell out you need to determine the value of your company. Also managing cash flows is extremely important; to generalize a finance person could argue that cash flows are much more important than making a profit. Strategic analysis courses would be beneficial to analyze an industry - if you are going to make a product/service to compete in an industry, knowing how to analyze what's going on would be of great service. I do not think it is really possible to take a class on how to become an entrepreneurial, but you can take a mix of classes to give you the skills to better utilize your entrepreneurial spirit.
Now if you do not want to take a plethora of courses - and many people do not - then you may want to do what the above poster mentioned and partner up with people from the business school. As I mentioned previously we have started a student organization to reach out across multiple programs and your university may have something very similar. . . or hell be an entrepreneur and start that club!