XP SP3/Vista SP1 issue - pwr mgmt?drivers?

Got about 25-30 Dell Latitude 830's here (all new). All running XP sp3 or Vista sp1. Have some HP's as well(don't recall the model).

Issue is:

After the machine has been left alone for some time (at least long enough for the screen saver to kick in, which by default is set to 20 minutes, but the delay required may be more than that 20 minutes), you move the mouse or hit a key to clear the screen saver. The screen saver immediately goes away, leaving you with a blank desktop or blank wallpaper with a mouse pointer. At this point, you would expect to see a dialog box with the title "Computer Locked" that says "This computer is in use and has been locked. While it's in this state, the machine is not frozen: the mouse pointer will move, and the machine can be accessed over the network.

If you wait long enough, which I've found to be on the order of 30-45 minutes or so, you will eventually see that "Computer Locked" dialog box, provided you move the mouse occasionally to prevent the screen saver from kicking in again.

At this point, you can press Ctrl-Alt-Delete. However, nothing will change for another 45 minutes or so. After waiting, you'll be presented with the "Unlock Computer" dialog where you can enter your User name and Password. At this point you'll (immediately?) see your desktop again.

Other behavior I've noticed: Launching new programs takes a very very long time. For instance, you can run regedit.exe, but you won't see a window appear for a very long time. If you run Task Manager or Process Explorer, you'll see the regedit.exe process exists, but it does not have a window yet. I've also seen where you can launch cmd.exe and you'll get the black cmd window, but it takes a very long time before you actually get the C:\ prompt inside that window.

While the computer is in this state, there is no excessive disk activity, nor is the CPU busy. (I checked disk activity with the LED. I checked CPU by running pslist from a remote computer. The CPU showed almost 100% idle.)

The machines I've seen it on have been configured to not go to sleep when on A/C power, which is why I say it doesn't have anything to do with Power Save/Sleep mode. You could argue that it has something to do with the display going to sleep, but I know I've had at least one case where it happened before the display went to sleep.

I ruled out the image, as well as most of the software in the image (such as Nortel Contivity, etc). On Monday I formatted a D630 and took a Microsoft XPPro+SP3 CD and installed a totally default version of XP on it. I installed four drivers from Dell: Network, Chipset, Video, Audio, as well as the Notebook System Software. I didn't install any Microsoft updates. The only other setting I changed was the power settings so it wouldn't go to sleep. I joined it to the domain. The next morning, the machine was in that same state I described above.

So far, it appears that the problem will not occur if the machine is not joined to the domain (i.e., it's in a workgroup).

ANY THOUGHTS? ANY HELP?