Presario S4200NX - drag & drop problem

When I drag & drop files with Windows Explorer (XP Home) on my new Compaq
S4200NX computer (just had it a few days), frequently they go into the wrong
folder. It's always one folder above or below the intended folder on the
screen. In one case when I dragged a group of files, it transferred all
except one of them, so I had to drag it a second time. I'm also getting some
very sluggish behaviour in Windows Explorer. There aren't any permanent
freezes, but frequently it hangs for a long time just by clicking on a
folder, perhaps for a minute or so, usually with an hourglass or
intermittent hourglass, but occasionally without the hourglass. This slow
response isn't limited to Windows Explorer, although it's most noticable in
Windows Explorer. In one case Outlook Express hung for several minutes after
first opening it. Moral: have patience, I guess, and just wait... (:

Note: I first noticed this drag & drop problem after getting all of the
updates from Windows Update last night. I didn't notice it before that. This
box apparently came with software that's about a year old and there were a
LOT of updates! The security updates alone came to 45 MB. Then there were a
couple of drivers and a dozen XP updates, and I selected almost all except
the big .NET one.

I'm guessing video/graphics driver problems. Guess I'll have to go looking.
Hope it's not an overclocked processor or motherboard problem. Any
suggestions how to narrow it down?
Euc1id