Keynote does not have flowchart connectors like PowerPoint does. If you need this capability, your best bet would be to use a third-party application like
OmniGraffle or
ConceptDraw, although neither of these are inexpensive.
I have discovered a similar functionality to the rudimentary charting in Powerpoint in Numbers '08. If you use the Insert menu you can choose shapes. They are not nearly as pretty as those in OmniGraffle, and you give up the ability to do anything with Visio imports, but it is included with iWork.
The workaround is to create your flow chart in PowerPoint, copy and paste it into Keynote. It will then work like any graphic element.
Otherwise, create your flow chart boxes, place them in their positions, then use the line tool to create the connectors. Use the copy and paste function so you don't have to create each individual connector.
Keynote allows you to center and register your graphic element (in this case, connectors) quickly and visually with guidelines that automatically appear to indicate its position in relation to another graphic element.
Please check out my example at "http://dogzenart.com/keynote/InventoryFlow.html"