Upgrading infected Win XP to Vista Ultimate

"For starters, a few pointers - Unless you already have paid for the licence, I would seriously look to buy and install Windows 7 instead. Also, if the machine is infected with a virus, I would have a good think about simply backing up your files and installing from scratch.

If however, I have not put you off (and again, I would really recommend it), I would follow the steps that I wrote (and others edited) in the general Anti Virus advise thread.

To get rid of them,

Start with a good tool such as Spybot Search and Destroy or Malwarebytes Anti Malware and perform a full scan.

After this has finished, use Microsoft / Sysinternals Autoruns and look through most of the tabs (you especially want to pay close attention to Logon and Scheduled tasks) and delete most of the items that you think are viruses or research them first.

Next, protect your system with a good antivirus. I personally recommend Microsoft Security Essentials. You can also find a list of free antivirus solutions at this other question.

Also, it should be noted that some malware is very good at avoiding scanners, it is possible that once you are infected, it can install rootkits or similar to stay invisible. Sometimes, if things are really bad, the only option is to reinstall the operating system from scratch.

I personally do a few runs of Spybot Search and Destroy. If after 3 runs, it is unable to remove an infestation (and I fail to do it manually) I would go with a reinstall."