A tutorial on creating Scheduled Tasks in Windows XP can be found here. As for whether or not it's worth purchasing, that's up to you. The definitions used by the Pro and Free versions are identical, however, with the Pro version you don't get scheduled scans or automatic updates and of course you don't get realtime protection. If you are willing to run the scans manually and don't want the realtime protection or automatic updates then the free version will work for you just fine, but if you want any of those features you'll need to buy a license. There is no way to schedule a scan with the free version, even through the Task Scheduler, because SAS does not use commandline parameters to tell it to run scans, all you could do is start the SAS process which would not perform a scan.