Problem with ThinkPad memory?

I have an IBM ThinkPad Lenovo T61 with Vista. Yesterday I had around 48Gigs of free memory and today it reads at 36Gigs and I have tried looking at it several times and it still says 36. How can I get an accurate reading of my memory or my computer can get a reading on its memory. I have ran antivirus software and didn't install or download anything in the time where my "memory went missing". Thanks for any help..

Problem with ThinkPad memory?hijackthis

The best thing to do is use a software called ccleaner it will help a lot with freeing space and it can also help the computer run faster and more efficiently. It will also clean the registry.

Problem with ThinkPad memory?malware

http://www.download.com/WinDirStat/3000-...

Find it with this!
Your "memory" usage will fluctuate in day to day usage due to temporay files being created and not deleted, system restore points being created etc.
Memory? sound like hard disk space. You lost more than 10gb in a day. What you can do:

1. Check every folder for unknown file

2. Search all files and sort by size and see the largest file,

3. Delete all files under temp folder, internet cache and recycle bin