My 2 bob, a multi pronged approach is needed.
ewido is good but takes up system resources, so use and uninstall after each use (once a week or whatever - regularly).
Also try spybot - search and destroy (free)
Ad-aware SE (free)
Kaspersky anti-virus (free months trial) - probably worth purchasing as Norton is complete crap. Get rid of Norton if you have it. Kaspersky very good, i use it. At least use the free month trial. You'll be surprised what it finds.
Spyware doctor if you're really dedicated. Costs, but again is very good. Similar situation to ewido in that it uses a lot of system resources, so install-use-uninstall.
Generally speaking, uninstall all superfluos programs from your system. Things you don't need or use. Ideally you want to run your sytem as mean and lean as you can, from a performance perspective. Should you be need it i'd recommend using "hijack this", but we're getting into details here and you'll probably find that if you use/run the above mentioned tools you'll fix the problems.
Best of luck.