Open Vegas Pro, drag the source, and the base into your timeline.
Go to File, Properties, and Ruler, and set the ruler time format, (BPM) to 140.000. Also, mainly if you're in Sony Vegas Pro 11, you'll need to disable the "Quantize to Frames" feature. All of this will help you get the timing right.
Follow this chorus pattern: 11_11_111_1_1_11222_2_222_222_2