The indexing is for finding text on your harddisk. Unless you need to retrieve documents based on certain words/phrases regularly, this is an absolute waste of resources. This indexing starts the moment you boot, and keeps on for the duration. Stupid really...
There's no program I can think off that needs indexing for updates.
On all the PCs that ever went thru my hands, I turned indexing off, and ALL of them benefited from smoother running.
Get a copy of the latest HijackThis, and post a copy of the scan-file here as an attachment with the .TXT extension (NO Word-doc please).
I can then tell you what else you can turn off.