How to get started with minimum investment ?

That depends entirely on what your first business is. Here are some thoughts. I would recommend that you don't spend lots of energy on worrying about how little money you have. Instead, use the money you do have wisely. Budget, budget, budget, and then re-budget. Have fun when budgeting. Budget many different scenarios. And remember, when you budget, don't just budget the money you have - budget money that you anticipate will be coming in, so that when it does (and it will) you know where to allocate it.

If your business is one where you are providing services (e.g. you're a graphic designer or a programmer or a consultant of sorts), start with only yourself on the team and try to do all the jobs for which you would later hire staff. Market yourself using free methods (word of mouth, twitter, facebook, blogs, send offers to companies by mail or email). Give yourself a fixed salary for the first period (6 months to 1 year) so that you can invest the rest of the money you're making back into your business.

If you need to invest money in equipment or you need to purchase items to sell, always start out small - buy the smallest bulk you can, even if this means you're paying slightly higher per unit than you can if you bought larger quantities. Evaluate your risks. What's your worst case scenario? Can you liquidate easily? Do your items have an expiry date? Can you sell them back? And if you, at what prices?

Another option is to seek out investors. This is far more complicated than trying to start out with your own limited money at first. Before you can do this, you need to tighten your business plan and perfect your profit & loss projections. No investor (unless they're your family perhaps) will venture into risky business, especially not with today's economies. Depending on your country's banking rates, you will need to offer very competitive returns. You'll also need to hire an accountant or financial adviser. I would personally discourage seeking investors if you're a new entrepreneur. Being in debt is much worse than starting out with a small capital.

There is a lot you can do today with open source and social media to build your product and market it for close to $0. Try to find co-founders who would work for equity instead of compensation, skip all the unnecessary legal set up, heavily use open source and most importantly use agile development techniques, they will allow you to quickly launch and iterate, and maybe even fail quickly and cheaply and be ready to build your next one.

Regarding seeking investors, don't do it until you have a product ready with users. This is when you will be able to get a good deal on good terms. For now just focus on building your product and team, then launch as early as possible and test in the open, and use open source