What percentage of american households with grade school students
(K-12) have computers?  Of those households that have computers, what
percentage have broadband, dial-up, or no internet service?

I was not able to find exactly what you were looking for, but this
should be useful in answering most of your questions. There are some
relevant statistics next the the asterisks*

http://www.census.gov/prod/2001pubs/p23-207.pdf
*2/3 of households with a schoolage child (6 to 17 years) had a
computer, and 53% had internet access.

Is the United States Falling Behind in Adopting Broadband?
http://www.cbo.gov/showdoc.cfm?index=5082&sequence=0
*December 2001
*78 million internet connections in the US
*Broadband subscriptions - The United States had 27 subscribers per
hundred population

October 2003 Bandwidth Report - US Broadband breaks 40%
http://www.urlwire.com/news/102703.html
as of Sept. 2003, 
*49.7% use 56k modems
*7.5% use 28/33.3Kbsp modems
*2.8% use 14.4kbps modems

Internet Access in U.S. Public Schools and Classrooms: 1994-2001
http://nces.ed.gov/pubs2002/internet/3.asp
*1996: dial-up internet was used by almost 3/4 of public schools with
internet access
*2001: broadband was used by 85% of public schools to access the internet

The Broadband Revolution:How Superfast Internet Access Changes Media
Habits in American Households
http://www.arbitron.com/downloads/broadband.pdf
*36% of broadband households have children 12years and younger.  This
compares to 28% in dial-up households.

More Statistics
http://www.ntia.doc.gov/ntiahome/dn/html/execsum.htm

Broadband Adoption at Home
http://www.pewinternet.org/reports/reports.asp?Report=90&Section=ReportLevel1&Field=Level1ID&ID=392

Parents Online
http://www.pewinternet.org/reports/toc.asp?Report=75

3 out of 4 Americans have access to the Internet
http://www.netratings.com/pr/pr_040318.pdf

This is a pretty good collection of links.  I would accept this as an answer.