Adding to what you have already said and it being or should be common sense not to engage in inevitably what will infect one’s computer system. There are some useful tools within XP Pro and I assume Windows 7 that allow one to explore what is going on within the system, i.e. Task Manager weak in so many ways but one can glean some information from it, using commands such as msconfig, regedit and others. Plus with the myriad of really good and easy to use utility tools such as Norton System Works Pro you can keep a head of the game. One of the most important tools is setting a Set Point once a month and backing up before things go awry. Worst case scenario which is so only if your software is illegal, is to wipe the drive clean and start anew but first back up your data files and configuration files too.

Cheers.