Yes, you can take a cutting, even from such a small plant. However, you'll end up with a larger, healthier plant if you simply transplant your baby to a much larger pot - or into the garden. When transplanting, just chop off its head, don't take the cutting. The fewer operations you do during a transplant surgery, the less likely the plant will go into severe shock. You may not need to chop off its head, actually, but I always remove that new growth when transplanting. That way the plant puts more effort into its root system - a healthy root system, with lots of space to spread and feed from makes for a healthier plant overall.

In your shoes, I'd transplant that poor little thing ASAP.

Check these out..

Here is a link that might be useful: Basil cuttings

Here's an article I wrote about Growing Basil. You have plenty of time to grow your basil from seed, and if you are starting veggies, basil is even easier from seed. Your wasting your time taking cuttings from basil. Basil will germinate in 3-4 days if you have fresh seed from a reputable supplier. You can get great varieties of basil seed from Johnny's seeds(www.johnnyseeds.com)

"How to Grow Basil From Seed To Market Packs"