suzie,
What kind of caching are you talking about?
Are you planning on storing the data into a SQL database? If so - SQL Caching may or may not be required dependent on the number of visitors to the site, as well as what with your server is more efficient, i.e. SCSI disks have a very fast seek time making disk caching of very common SQL queries (verses a low SQL server) a good idea, however if you are on a virtual host environment with a dedicated Database server, it may just be easier & faster to have the info stored in the database..
Let us know what kind of caching you are planning on doing, and what BASIC architecture (i.e. PHP + MySQL + Apache + Linux, etc) you are planning on using, then we can make recommendations to suit the needs.
It would also help if you are able to estimate the number of hits you are targeting, and be realistic.