Make money on the net with zero investment ?

Yes it can be done, just need knowledge's to start, time to spend and maybe Money. But hey I'm talking about free money here. So you can leave the money parts for now.

1. Buy a Domain name and web hosting (optional)
2. Create a Blog, you can start with using Wordpress, or blogger
3. Check the news, and sites like yahoo for hot topics
4. Write about 5-10 related Topics per day
5. Submit each blog post to digg.com, buzz.yahoo.com, and other social media sites
6. Put adsense in several spots of each blog post
7. Sign up to a CJ.com and have an account and search for products related to each blog post you make. If there is a product then use your affiliate link and recommend this product.

Do this on consistent basis and do this for a solid year straight, you will be making at least $25 per day. And it doesn't takes long, Maybe 3-4 hours out of your day?

Note: IT IS NOT a "GET QUICK RICH SCEME". But it will give you an idea as a starting point on how to make an income on the internet.