It depends on which internet browser you're using. I use Mozilla (Netscape) and the files that accumulate on your HD depend on the cahce size you set in the preferences for the browser. In Mozilla or Netscape, the cache files are stored here:
/Users/User_Name/Library/Mozilla/Profiles/default/slt6sitx.slt/Cache/
I don't know where M$ Internet Explorer has its cache files, but they might be here:
/Users/User_Name/Library/Preferences/Explorer/Temporary\ Files/
I think IE has one large file, whereas Mozilla and Netscape have MANY MANY files.