Audit your computer with Belarc Advisor, Antimalware essentials
Removing the Google redirect rootkit, solving a bigger proplem
Viruses and spyware are like cockroaches. In the early days if you opened the door they occasionally came in. Now they're a foot deep. They pour in if you open the door and find small cracks if you don't. The two problems are separate. Anti-virus programs don't protect against spyware (and vice-versa).
If you have a virus (out-of-date anti-virus program), begin with "Housecall" (Trend Micro). It finds and removes viruses. There's now good anti-virus freeware - AVG (Grisoft). Install it and keep it updated! New! - For stubborn malware try Malwarebytes, a freebie which is compatible with standard antivirus and antispyware programs. Use only one antivirus program! How to get rid of downloader.agent.11.Q. rasauto.exe problems, Smitfraud, easysearchbar, clicker.fr
Finding invasive files
Regularly check the Task Manager (ctrl-alt-del); delete strange files. If they're active you'll have to reboot in safe mode; press F8 (in XP) during reboot. Download Hijack this. It surveys active files and permits selective turn off. Look at files in c:\windows\prefetch. Note datestamps; suspect (.exe) files coinciding with the appearance of problems. If in doubt google file names. If doubt remains, change the name of the file; this allows you to reactivate it if necessary. Keep in mind that malware often generates files with random names. Search for names of bad files in the registry. I use Registrar Lite (freeware). Delete entries that refer to undesirable files. Recently I've had trojans which leave .exe files in SYSTEM32 with apparent memory addresses in parentheses. Find these near the top of the folder, delete them.
Install Spybot, check for spyware, and "immunize". Avoid anti-spyware programs that appear in pop-ups. They often install spyware. Unfortunately there's now spyware that Spybot won't delete. See how I got rid of Vbouncer. For hidden software running in the background, restart your computer in "Safe Mode" (Press F8 during restart). "Hijack this" detects malware running in the background. Delete nzsearch.
General computer maintenance
Defragment regularly. If defrag hangs up, you likely have viruses or spyware running in the background. Minimize startup programs (for Windows 98). For both Windows 98 and XP the "msconfig" utility (click on "run", type in "msconfig") helps do this.
If you're continuously connected to ethernet, you need a firewall.
For specific problems, google. Somebody has had your problem and solved it