OK, so "Available: 200" would seems to indicate that the memory really is being used and it's not just a side effect of SuperFetch.
When you say the memory fills up while "the program is being installed", what program are you talking about? Are you really installing it, or has it already been installed and you're just trying to run it?
Zoron's question about the page file is a good one - if you tell us the "Commit (GB)" figures from Task Manager that will tell us how much page file you have (if you have 4GB of physical RAM and the 2nd number is, say 6, that means you have 2GB of pagefile space).
In the Task Manager window / Performance Tab, click on the "Resource Monitor..." button at the lower right, then click on the "Memory" tab of the Resource Monitor window that opens up.
Click on the "Working Set (KB)" and "Private (KB)" column headings in Resource Monitor to see which processes are using the most memory.