Catalog Files for Indexing Service.

This used to be in my disk cleanup dialog box along with Downloaded program files and tmp.int.files. etc.and seemed to disappear after i downloaded the MS .net framework.I have winxp,sp2,G-way 503GR,HT,3.0ghz.This is still on my brothers pc which is almost the same as mine which is why i am puzzled.I am not sure if this is important when it comes to diskcleaning and don't know why it would just disappear.Any help would be appreciated!