microsoft powertoys has a free camera thing that will save a picture every X minutel, i downloaded it awhile ago and used it like that. this should work perfectly for you.
http://www.microsoft.com/windowsxp/d...powertoys.mspx
it's a microsoft product from there website, soo the download is no more dangerous than your current windows version.
download link is at the bottom, "Webcam Timershot"