Hi! I followed the advice of an earlier answer (http://www.radicalreference.info/node/1092) and went to http://www.firstgov.gov and searched 'immigration statistics.' This led me to the DHS Yearbook of Immigration, which seems to include fairly robust historical data: http://www.dhs.gov/files/statistics/publications/yearbook.shtm. If you click into the 2008 yearbook, a 110 page pdf, you'll see historical data for 'enforcement actions' starting on page 99.

As the previous answer suggested, changes in terminology and classification means that there will be some variation in data categories. But you should be able to get a start here. I hope this is helpful.