Glossary of Statistical Terms
This excellent site can help you whenever you have a question about a statistical term.
http://www.stat.berkeley.edu/users/stark/SticiGui/Text/

Statistical Resources
The University of Michigan Documents Center has an excellent site of Statistical Resources on the web. You might wish to explore the richness of this site when you have time, or look up a particular item if you are having trouble.
http://www.lib.umich.edu/govdocs/stats.html

Quartiles
Discusses quartiles; click on "Next slide" for an example.
http://www.business.utah.edu/~mgtsc/Ch03a/tsld015.htm

Percentiles
http://sleeptight.com/EncyMaster/P/percentile.html
http://badame.vse.cz/cs/toKEYBCS2.cs.cgi/mirrors/hyperstat/A79766.html

Weighted Percentiles
An interesting interactive site calculating percentiles for the weight of children.
http://www.blubberbusters.com/height_weight.html