I went to the IRS website and found a great excel sheet that lists all of the government's income:
http://www.irs.gov/taxstats/article/0,,id=96380,00.html
I added a simple formula that calculates the percentage of total income taxes (excludes employment and estate taxes) that comes from corporations versus individuals.
There's a consistent pattern here. Some numbers in brief:
Corp Individual
1969 28.2% 71.8%
1970 22.1% 77.9%
1980 20.1% 79.9%
1983 15.0% 85.0%
1989 18.5% 81.5%
1992 17.5% 82.5%
1996 20.2% 79.8%
1992 17.5% 82.5%
1999 17.8% 82.2%
2001 13.7% 86.3%
2002 16.9% 83.1%
2003 16.4% 83.6%
So, by estimates, I figure that when Bush is out of office in (good god) 2008, corporate taxes will be HALF what they were (as a percentage) in 1969, or roughly 14%.