Taking off work during the holidays always poses a challenge, especially if you hold the rank of "newbie." Claiming those coveted hours poses a greater challenge if you've used all your vacation time. Still, no time off doesn't necessarily mean you can't take time off and keep your job. According to Salary.com, many employers are willing to negotiate vacation time. However, you may have to "forego other forms of compensation" in exchange for more time off.
Pick the best time: As a business owner, I can attest that timing is everything, especially when you (the employee) want a huge favor (like time off when I need you). Asking me for two extra vacation days during an end-of-the-year audit seems exceptionally selfish. Word of caution, you have to pick a good time to make your request. For me, that means not on Monday or Friday or when I have an office full of people.
Cover your ground: Employers feel better about granting extra holiday time if they know things won't fall to pieces while you're gone. I agree with the guys on The Hired Guns; don't expect an employer to give you more time if it puts them "under the gun." You need to close out your open tasks and stay in touch while you're gone, in case something goes awry. Just like asking for a raise, timing is everything.
Give something up: Check your work stats and offer to give up some flex time, sick days, or another benefit. A trade-off is a reasonable request as long as it involves time or benefits from the current year.
Find a replacement: Talk quietly with trusted coworkers about your dilemma. You'll have better luck getting permission to take off if you have a replacement ready. However, don't stir a hornets' nest by talking to everyone in the department; just try a select few friends.
Meet a special goal: One way to curry a little favor is to meet a special goal. Suppose you actually do sell 30 widgets in a month, what's in it for you? Make a deal with your boss. Tell him you'll make a special goal or achieve a special task in order to have the time off. Then get to work!