There isn't anything that comes with the MacBook that fits what you are describing. However, there are a number of apps available that could work depending on how intensive your paint needs are.
For instance, if you need max editing, you can use
Photoshop. This will run in Rosetta on the MacBook & is reasonable performance assuming you're not running massive filters every other second. There is also Photoshop Elements, which is a stripped down version.
If you just need to simply add some graphics to a document, you could try
iWork, which is Universal. There is a demo that should come with the MacBook for 30 days to try out.
If you need more of a diagramming tool, I'd suggest
OmniGraffle, which is also Universal.