That might very well be the culprit. The drivers you get during the Windows installation are for you being able to get the "real" drivers.
It's not an easy task to find the Win7 drivers, though. There's a lot of driver download sites, but I don't trust them. Same goes for automatic driver installing programs. Getting them from the motherboard manufacturer would be the best alternative but I couldn't find any site based on what your DxDiag told about the computer. The closest I could find was
http://panam.gateway.com/us/en/emac/product/default.aspx?modelId=1628 but the site looks abandoned, most of the links didn't work.
The safest way would be to look for the manufacturer data in Device Manager and opening the Properties for each and every System device, not to mention those with an exclamation mark. Under the Details tab/Property drop down menu find Hardware Ids, copy the PCI/VEN value and google for it. You should soon find some information about the manufacturer and model of the devices. Then "just" find the right site to download and install the drivers.
An educated guess is that the chipset is made by nvidia so once you find the model you should get a whole bunch of system devices covered by a single installation.
Hope this helps, it's hard to give a 101 for obsolete hardware with that poor manufacturer support.