C&B,
When you run the antivirus and spyware scans make sure they are set to thorough as a basic scan can miss things. I would also set the scanners to search archives if your program supports this. I feel the prob is most likely related to 1GB of RAM as perhaps newer programs or updates you have installed are taking more RAM than before or the CPU may be working harder than usual. All windows installs get slower over time and it can get to the point where a re-format and re-install are required.