Thank you all for your answers.
So now that I've read many different opinions on whether a simmer could actually fly a real 737 or not. Some of you said I could under very specific circumstances and/or with a real pilot next to me, and others said I couldn't, because the feeling would be very different and much more would be to take into consideration during a flight. Before I tell you in what I am believing now, I want to get something off me: I read some posts here of people saying something like: "Oh god, not again a noobie-flight-simmer who thinks he could fly a real airliner...". It's true, I am really just a beginner in flight simulation compared to other people and yes, that is the reason why I am asking this question. I mean, I was so incredibly stunned of how complex it is to fly a plane and how good and detailed the simulation was. Then, suddenly I had my first simulated landing on a 737 and it was amazing considering the highly complex procedures I had to go through. Now I'm wondering of how could anyone, who had his first landing, didn't want to know if he could do that in real life too. Anyone who says he wasn't curious, is a liar, in my opinion ;D
Now, thanks to your posts, I think that I could do a startup, taxi to the runway on a big and empty airport and maybe, under very good conditions, depart from that airport, all with a bit of instruction of a real pilot next to me. Handling the autopilot during the flight wouldn't be any problem, I think. But, I would leave the landing for the real pilot. I think that I could do all that, if nothing special would happen. To know what to do in special situations depends all on experience.
Thank you all again for your answers.