My thought is that is is not likely the PSU.
Can you tell us more about it, though?
How many Watts?
Some video/audio programs are more intense about system resource use than others.
1.5 Ghz isn't bad, but it's not 3.2 Ghz for instance.
512 MB isn't unlimited ...
Onboard video isn't a video card ...
Doesn't the TV tuner card use system resources like the onboard video also does?
For best information I always suggest using a free download
that details system information in a case like this:http://www.snapfiles.com/get/everest.html
Post again with any additional information that you can provide after viewing the report, perhaps. That program does give recommendations in key areas if it finds conflicts/deficiencies. It also details much more.