Arstechnica has an article on the Win 7 memory issue, and they report it's not really an issue after all. The XPnet testing apparently includes all the RAM being used - not just the stuff being held in your RAM as preloading. The preloaded stuff can be quickly dumped to free up RAM and aren't really considered to be part of not-available memory. It's just used to speed up the system, but the XPnet tool doesn't quite understand this.
arstechnica.com - I installed the XPnet performance monitoring tool and waited for it to upload my data to see what it might be complaining about. The cause of the problem was immediately apparent. It's no secret that Windows 7, just like Windows Vista before it, includes aggressive disk caching. The SuperFetch technology causes Windows to preload certain data if the OS detects that it is used regularly, even if there is no specific need for it at any given moment.
Full article here.