generally programmes which runs automatically upon system startup. The usual suspects are chat programmes like msn/windows live messenger, skype, icq, aim, audio programmes like quicktime/iTunes's bonjour, adobe acrobat reader updater.

Some manufacturers would also have their respective programmes to auto-run due to certain hardware needs (may/may not be necessary) like harddisk drop sensor, audio studio, optical auto-disc detection.

With all these, couple with Vista, if your laptop doesn't not have sufficient memory/ram, it'll start running low on resources.