Some installers allow you to specify whether to install 'just for you' or for 'All users'. However, not all give this option so I suspect this isn't the case with the software you've installed.
If it does install for 'All users' without asking you, you can hide access to these programs by deleting or moving shortcuts from various places.
Move shortcuts from :
c:\documents and settings\All Users\Start Menu\
to :
c:\documents and settings\YOUR USER\Start Menu
Delete shortcuts from :
c:\documents and settings\THEIR USER\Start Menu