I would second Car's recommendation for the site.
Personally, and from feedback for 'techies' (I'm not one at all) AVG free, Superantispyware and using Firefox as opposed to Internet Explorer seems to insulate you from a load of hassle. None of this costs you a cent.
For particular problems, in the past I have contacted Adwareaway (not to be confused with similarly named sites/software) and have found them to be excellent. Some problems fixed by their freeware, some needed full version but it was very cheap and well worth it - twice, I had malware problems that at the time no other crowd could help me with - they fixed it in minutes.