What were you doing whilst this is like that, listening to streaming audio, video, just browsing, etc. ?
What is your browser ?
You can click the avast 'a' icon, which will open the On-Access Protection screen, if you see a button Details... click it and you will see icons on the left. Select the Web Shield icon and click Terminate, you will be asked if you want to persist the changes, for now answer No or it will continue in the next boot.
These are my current TM readings and I too have XP Pro, Firefox, web shield enabled and just browsing on the forums. The VM Size we have been informed provides a more accurate figure of memory use, though the Mem Usage is 39,900 way, way lower that the 191MB figure yours is showing.