Not Enough Memory Available Message

I am having a lot of trouble getting my computer to stay on for more than a couple of hours ever since installing Windows 7. Since I got past reinstalling all my programs and started actually using the computer I noticed these error messages coming up when I was running iTunes and firefox at the same time. After a while of testing I discovered that in fact iTunes alone was enough to trigger the message. I have since discovered that in fact I don't need to be running anything, and the memory still runs rampant.

At first I thought this was a virtual memory issue. I tried turning that off, which made it worse. I then tried spllitting my virtual memory evenly between my non-system drives. This helped quite a lot, but still the computer will be unuseable after only a couple of hours depending on what I am doing. Eventually if try and continue using the computer the screen will just go completely black.

I have found that in Resource monitor even when I don't run any programs my 'modifed' memory and to some extent my 'In use' memory just climb and climb. I also note that wmpnetwk.exe appears to be using more than its fair share. It drops back every so often, but I have seen it climb to more than 1.5 gig while the system is idle. At the moment it has 4,002,098KB under 'Commit' and 1,155,960KB under 'Working Set'.