I had that exact computer and no problems running Sentinel on it except one time. Turned out it had some malicious stuff using all the ram. once cleared using Spybot S&D and doing a scan with the antivirus scanner it ran fine again. So I'd check those items plus make sure you have plenty of virtual ram and that should take care of it for you.
I have several machines I run Sentinel on and even the one GB machines load it quickly, just a few seconds.
I'd suspect something else that's using your memory up. Also how much virtual memory do you have? That could be part of the issue.
Turned on computer today and time went down to 17 seconds. Did some file cleaning and computer got an update of some kind. Maybe what was needed to speed things up.
On the other hand, today I fired up Sentinel and clicked on update data base. It says that it has the latest, which was back on Oct 13. Is this normal that there are no updates to the RR database and thus display this message?