I'm looking for demographic information on 18-30 year olds
(specifically 18-30 year olds in the U.S.).  Here is what I am looking
for:

1.  Total number of 18-30 year olds in the U.S.
2.  Growth of the 18-30 year old population (e.g. how many 18-30 year
olds will there be in the U.S. in say 2008?)
3.  What % of 18-30 year olds are male vs. what % are female
4.  What % of 18-30 year olds use the Internet?  What % have broadband connections?
5.  What % of 18-30 year olds own a DVD player?

I don't need answers to all of these questions in order to be
sufficient.  Rather, answers to at least 3 would be fine.  If you can
answer more I'll reflect it in the tip.

Wow, that's a pretty involved question.  But here is at least a partial answer:

1. According to the U.S. Census (http://factfinder.census.gov), in
2000 there were a total of 46,524,790 18- to 29-year-olds.

2. According to a U.S. Census population projections document,
http://www.census.gov/population/projections/nation/summary/np-t1.txt
, the approximate percentage increase in the TOTAL population between
2000 and 2008 is 7%.  If the rate is the same for this age group,
there will be 49,781,525 18-29-year-olds in 2008.  Note that a more
detailed analysis based on birth rates and other information would be
needed for more accuracy.

3.  In 2000 there were 23,672,589 males age 18-29 and 22,852,201
females. That's 50.88% male and 49.12% female.

4.  Check out these articles for some information on internet usage. 
They're not exactly what you're looking for, but should give you an
idea:
Online activities by age:  http://www.infoplease.com/ipa/A0903376.html
Internet usage:  http://www.infoplease.com/ipa/A0901651.html

5.  Here is an article on overall DVD player ownership:
http://www.rtoonline.com/Content/Article/Jul03/StudyDVDUsage071803.asp
55% of U.S. households can watch DVDs at home; however, only 16% of
all households have a separate DVD player; the rest watch DVDs on
computers or game systems.

I found a number of market research companies that are willing to sell
their information, but all are pretty expensive.
http://www.parksassociates.com/reports&services/reports/tocs/entertainment.htm
http://www.marketresearch.com/product/display.asp?productid=932260&xs=r
http://www.ipsos-insight.com/tech/publications/tempo/tempo_2003TOCq1.cfm

I hope this helps!

Works for me for an answer!