Riten,

No, you do not have to register a business or get an EIN to work under 1099. You will work using your SSN. The only difference working as a W2 contractor vs a 1099 contractor is that you have to pay the employment taxes on your own on the latter which otherwise your employer would have paid.

When you are an employee or a W2 contractor, employers generally withhold taxes on your behalf. Additionally, employers also pay the same amount of taxes to Fed that you pay from your paycheck.  Now since 1099 contractor is considered as self employed not only you will have to pay your taxes but also pay the taxes that employers would have paid to Fed for you.  You need to make these payments quarterly.

So, overall, there is more paperwork and hassle that you need to take care of while working on 1099. However, you will be able to deduct certain qualified expenses while filing taxes as long as you save all the receipts. The expenses may include purchase of a computer for your contract work, money spent on gas etc.

Good Luck 1099ing :-)