Vista - Random programs suddenly stop working--"Not Respondng"

System is Asus M2R32-MVP mb with AMD X2-5200 CPU, 2x2GB
memory, Seagate 320GB SATA2 HD, and nVidia 9600GT PCIe video
card. Cleaned PS and checked system recently, no problems
found. All current patches installed and no problems there.
BIOS is current.

I mostly play one online game and also do a variety of
online news reading, e-mail, and use MS Office 2007
(Home/Student), etc.

Several times a week (or more), a program will just suddenly
stop responding--no notice or warning. No keys or mouse or
buttons for the program functions work . C+A+D gives me the
menu choices and I check Task Manager. The program initially
shows as running--then it virtually always changes to "Not
Responding" and shuts down the program. Other programs
running at the same time are fine and keep running.

One program that stops the most is USB HDTV tuner, Hauppauge
HVR-950. Most frequently, the program will start (to record
a show), show the startup screen, then suddenly stop within
ten seconds of starting--and report it can't find something.
There is a lot of space on the indicated HD to store the
programs to be recorded, so it is not a full disk. I click
the "record" button and it works fine on the target disk.

I also notice this problem with Internet-related activities
(playing online game or using IE7, but it also does happen
with non-Internet programs (Solitaire, for instance).

The system runs 24/7, on a UPS. All USB devices are fine, so
is the network, and the eSATA drives.