Kat - and the couple of others with the homepage reset thing:
There is a fairly well known virus that does this, and a complete cleanout usually means using Regedit to get offending lines out of your registry. I'd suggest checking your symptoms with your AV provider of choice for instructions. This may not be spyware.
On the subject in general:
I'm about as offended as anyone about invasions of my machinery, but quite a few of the things commonly called spyware are at least "semi-legitimate" business tools, used by a number of sites for what they consider to be legitimate business purposes. Properly used, they're annoying, but not much more than just the "price of doing business."
It is illegal, in the US, for anyone to place "monitoring" software on your machine without your permission - but, they can be extremely sneaky about getting you to say yes without realizing you've done so. Most instances of adclick, doubleclick, fastclick - and most other stuff that AdAware detects are, technically legal things you've agreed to let them use when you visit their sites. You have to deliberately go get their privacy policy and actually read all the fine print to know. You can fight with it all you want, but every time you re-visit a sight that subscribes to one of these services, you'll get a new cookie.
If you click the "print" icon at the top of the first page, it will display the whole sequence of several related articles so that you don't have to step through. (It's about 10 pages, printed, but you don't have to print it). If you do print it, be reminded that you can usually set print options to print a table of links, in case you want to look at some of the links offline.
I'd strongly urge anyone concerned about this subject to read it.
One of the more insidious instances they cite is the use, by virtually all of the music download (MP3) sites, of imbedded spyware that cannot be removed without disabling the download program. If you have one of these programs on your machine, you are being tracked much more thoroughly, and personally, than anything you'll get from the traffic measurement cookies.
Most of the anti-spyware programs cited here, and in other similar threads, will do something, but most of them do very little to actually improve your privacy that cannot be accomplished by regular, intelligent, cleaning of your cookie bin. Some people, depending on surfing habits, may need more; but an reasoned understanding of what it is that you're fighting is a very important first step.
I'm seriously irritated by it all, but then I'm similarly irritated by the ... with the cell phone at the symphony concert.
Appropriate response isn't always very satisfying.