Try spybot but it may be a ok system but Vista is a resource hungry o/s and you only have 1GB of ram if you have onboard graphics that will be taking a chunk of it as well depending on what you have got it set to.
No wonder it is running slow. Minimum size for memory in a Vista machine is really 2GB but i would run it on 3GB.
Depending on the type of memory you can get a stick of 1gb DDR2 for 10 quid for a budget stick.
Hope that helps.