Windows Defender (free) will show you rubbish in the Start Up list (Startup Programs) and any phantom programmes that may be eating cpu/memory resources (Currently Running Programs)- you can remove any that are suspicious or unwanted.
(Windows Defender - Tools - Software Explorer)
CCleaner (free) has a feature to tidy up the registry.
Spybot Search & Destroy (free) will remove spyware.
Defragging the disk is also a good idea.
Peccavi, January 2009