In order for your Wacom Bamboo tablet to be able to draw pressure sensitive lines, you need to create a new pressurized brush in adobe illustrator. Here is how you do it:
1. Open brush window.
2. Select new brush.
3. Select ‘Calligraphic Brush.’
4. Choose it’s attributes.
We only need to set it’s ‘Size’ parameters.
Give it a name and choose some attributes. Click OK.
Then try drawing with your stylus on your bamboo pad.
Links that help