I know my setup isn't great or anything, but lately, it's been going very slow.
 
Dell Dimension 2400
P4 2.8Ghz
1GB RAM
120GB Hard Drive
DVD-RW and CD-RW
PCI Cooling Fan
NVidia MX4000 Graphics Card
Intel ExtremeGraphics Integrated
Dell 1905 LCD running at 1280x1024
Windows XP MCE 2005
 
I have the Intel card disabled, and I've had it disabled since I installed XP about 8 months ago.  Lately, I've noticed that my frame rate on everything has been crawling at about 5FPS.  It's unusable to use the Visualizer on iTunes or to do basically anything, even the low end gaming.  I use this computer as a server that runs 24/7 and have a bunch of "conditioning" software to make the computer more efficient like it defrags when the computer is idle, cleans out unneeded files once a week, scans for viruses daily, etc...  I have the latest Nvidia driver (6.14.10.9371) and the bios version is 4.18.20.39.13.  The fan is directly below the heat sink, so air passes the card continuously and the card is cool to the touch.  It appears that iTunes is using the CPU to render all the graphics as my CPU is at 100% when the visualizer is going (iTunes using about 95% of it).  Without the Visualizer, the cpu idles around 0-10%  
 
Thanks
 

 
I use an MX4000 in an office computer of ours.  I think I paid $19.95 and with rebate the card was $9.95.  That was 5 years ago.  The fact that it works to do word processing, light internet surfing, email and calender type tasks is all I use it for.  A game of solitaire is within it's limitations.  The fact your card seems slow to the point of running frame by frame is no surprise.  You are in need of an upgrade.
 
You ask:
 

 
MX4000 is the key to solving the mystery.
 
 

It used... to be better than it is now.  I did just work on bios settings and found that my Intel graphics chip was not disabled for some odd reason...  AGP Architecture or something like that was set to 64MB and I changed it to 256MB (not really sure what the AGP thing is, since the MoBo does not have an AGP card).  Also, the Onboard Video Buffer was set to 1MB, and I changed it to 8MB.  Now it's running much better with iTunes (46FPS) but youtube videos full screen are still unbearable.

Glad you got it working better.  On many MBs, when you install an AGP card, the onboard graphics disables or defaults to the AGP card.  I built a computer for a kid who was using an MX440 to game.  He sat at his computer for hours/days trying to play online with his friends one frame at a time.  He's happy since I helped him out.  He games with ATI 9600XT I got for him for $60 a year ago.