Missing memory

I have 4GB of memory for my machine. When I run a virtual PC, it is set up to have 1Gb of the four. Even when first starting, it shows usage of about 2.5GB in the "Perfomance" tab of the Task Manager. After not too long, it grows to a little over 3GB with the Virtual PC on. When I sum all the memory usage that is displayed in the "Processes" tab of the Task Manager (sorted in descending order of usage), I get only about 600MB being used. Where is all the missing memory? It really slows my machine. Here is a snapshot of [most of] the Task Manager screen.

I used Registry Mechanic and I went through the cleaning and compaction. That required a reboot, so now more is showing as free as I just brought the system up and started the virtual machine. However, even though not maxed out yet, there still seems to be a lot of memory missing. I have the memory ordered in descending order by "Working". I also see 770MB in "Hardware Reserved".

The list shadow storage came up with statistics for drive C. The windirstat said it was utility to look at directories. My problem is that my RAM is being used to the max. I have 4GB of ram. the list shadowstorage said that 9.2GB (0%) had been allocated.

Are we talking about the same thing?

Can anyone else offer a suggestion? I have no idea why, even after allowing for a full 1Gb for the virtual machine and the 770MB for the hardware, why the rest shows an additional 2.2 GB as opposed to the sum of all the processes which add up to about 500MB.

Could it be bad memory and if I were to replace the memory it might be better?

I already posted the results from the resource monitor. It is the third post in this thread.

So, you have 770MB reserved, which we're going to guess is an onboard video card (can you confirm?). It's not unheard of for the OS to take ~1-1.3GB of memory (mine does, consistently) plus the 1 GB you allocated for your VM. That comes within a couple hundred MB of the 3GB it's showing as taken. I'm not seeing much wrong here.