tbdi:

I don't know Vista since I still use XP.

It's interesting you post about problems.  A person from work called this morning to say she was having problems with her Dell with Vista notebook.  She bought it several months ago and everything was fine until a few days ago when she started to have problems such as Blue Screen Of Death, with an error message which is fuzzy and the words jumbled on top on one another, then the notebook reboots.  She also spoke of it checking for problems and that this happens frequently each day.

She bought Kaspersky 2009, an antiviral, anti-malware program, but thinks things got worse despite removing some of the pop-up windows and whatever else that began to occur initially.

Since I do not know anymore specific at this time, I can't say what is happening to either of you, but some thoughts include:

1. You've been infected.  It can happens even if you use a firewall and antiviral and anti-malware programs, some of which can hide from or infect these programs.  A suggestion is to let a remote site scan your drive (for free) such as found at http://temerc.com/onlnscnnrs.htm.  The Symantec/Norton link is my initial choice - it will need to load an Active-X file(s) before scanning and it may take an hour or 3 depending upon how much is on your harddrive.  The "a-squared" link may be nice to run too, since it might identify the problem.  After ID'ing a problem, use Google to find out what it is and how to get rid of it.  Or, ask a friend.  :-)
2. There is corruption of software such as the Operating System (Vista).  I know there are ways to repair and/or overlay fresh files from the XP Windows Installation Disk, but I don't know about with Vista.  You are under warranty so a call or internet tech support session might facillitate correction.  If you do the internet route, Dell can actually remotely control your computer and do diagnostics and fixes without any further input from you.  Scary letting someone miles away manipulate your computer but it is kinda cool and may work a lot faster than you brute forcing the issue.
3. There is malfunction of hardware.  This is definately a tech support issue since you are under warranty.  You might get a whole new notebook!
4. Windows, Dell or another application "pushed" an update onto your computer via "automatic update" and this caused conflict/corruption.  Inputing the precise error message and/or symptoms into a Google search may illuminate the problem.  (Google is excellent when used in this manner)
5. Running more than one antivirus or firewall can cause a boatload of trouble.  Uninstall (or turn off one firewall) any duplicate security applications.  I'd probably unistall all of them, reboot, then reinstall just the one I wanted to use.  Probably not your issue, but thought I'd mention it.  It would be wonderful if you could relate the beginning of your problems with the installation of a specific program or a change in the setp/parameters of the operating system.  Unfortunately, computers are evil and rarely give it up easily.  ;-)
6. If you still can't figure out what to do, or the solution isn't satisfactory, or you're tired of dealing with the problem, then save/burn all documents, favorites, emails, address book, photos, music and anything else unique you want onto a flash drive or a CD/DVD disk.  Don't worry about programs as you can reinstall them - as long as you have them saved too or don't mind re-downloading on the internet.  Once your irreplaceable data is saved off the harddrive, then use the installation disks to wipe the harddrive clean and reinstall the progrmas to their factory fresh state.  Dell usually keeps a hidden partition on the harddrive with a copy of the factory setup.  Call Dell or look in your User Manual for instruction on how to use the hidden partition to write over the drive and restore the notebook to the day you first started it up.  Unfortunately, this method will destroy all the programs and data you put on the harddrive, hence the need to save what is irreplaceable first.

I know this is all overwhelming.  The good thing is that most of these suggestions are relatively simple to do, though what you find on Google may be a bit complex initially. 

The best thing is that you are under warranty.  Think about saving all the irreplaceable (or PITA replaceable) data before monkeying around trying to fix things unless you are confident in the remedy.

Keep your spirits up.  You will prevail, one way or the other! 

Adblock Plus does a good job from what I've gleaned. 

I use Firefox occasionally and my Hosts file duplicates Adblock fairly much.

One thing I like about using a Hosts file is that you don't need to install or run anything else.  Hosts file is always live using Windows.

If you have free time to kill or you just like tinkering, check out the following.

I looked a bit at Hosts file use and Vista.  Seems the restrictions imposed by UAC (Users Access Control) makes it a little more tedious updating the Hosts file - http://www.mvps.org/winhelp2002/hostsvista.htm.  Fortunately, some enterprising youths have devised applications to work with UAC and automatically do the job - http://forums.cnet.com/5208-4_102-0.html?threadID=248156.

Personally, unless there was a strongly compelling reason to change, I wouldn't.