Pepe, you don't need to incorporate to build business credit. When you set up your business, whether as a sole proprietor or a corporation, you'll get a FEIN or tax i.d. number. This is essentially a SS# for your business and will have it's own account with the credit bureaus. Anytime you open a bank account or get a credit card or a loan using this number it will build credit.
You'll still be required to personally guarantee any credit extended to the business whether you're incorporated or not. What this means is that in building your business credit you'll also be rehabbing your personal credit. So unless your personal is beyond repair it won't be much of an advantage.
It takes two years to establish a minimum business credit rating generally. However, this doesn't mean you'll have an excellent credit rating at that point. Chances are you won't have much credit history since it's unlikely you will have been extended much credit during that time. Also, when it comes right down to it, good personal credit is worth more to a bank than good business credit. Just something to keep in mind.
I'm not saying that getting business credit is a bad idea. But, the assumption that building two years of business credit will compensate for bad personal credit may be a little flawed.