Help. Dying Cube?

[J. Torrey]

Hello.

A couple of days ago, I started noticing artifacts (black dots in 
distinct shapes) right around my mouse pointer.  It went away after a 
reboot.  Today, I've not only had that but the Cube is behaving 
erratically with major artifacts (one pixel lines running vertically 
across the screen about every 1.5" apart, etc.) appearing and major 
problems booting (like not booting after power is turned on).  I rested 
the Cube for a couple of hours, and now things are working (but for how 
long I am not sure).

I tried using the Hardware Test CD, but twice it locked up (one on the 
memory test and one on the mass media test) and failed to run.  Not 
very cool.  I also unplugged all of my USB and Firewire devices (except 
my 15" ADC flat panel screen and my keyboard and mouse), and also had 
the same problems.  I also moved the DIMMs around, took some out, etc.; 
that didn't appear to help.

Any ideas on what may be going on?  Also, is the Apple Store (one 
located near my home) a good place to take hardware for analysis and 
fixing?

Thanks,
Jason