Well, the problem is... It is a very generic message for the Standard VGA adapter, since it assumes that by using the Standard VGA adapter, you have a 'newer' that it does not have drivers for. All video cards will have the standard VGA support for that reason, to allow you to 'see' with the computer, but in order to actually get the full benefit of the card, you need the drivers that will allow it to run under Windows 7 properly.
In this case, your S3 Chipset might not be supported as it is an older chipset. You COULD try here:
S3 Graphics - Products
That's the S3 Graphics website, but the problem is, your motherboard's description of the integrated S3 Chipset is vague or outdated. Looking at S3's Site, which seems to point back to VIA, there is no Windows 7 Driver for the Unichrome chipset you may have. Not even a vista one.
At this time, your three options are this:
1) Try and search for drivers for the P4M800 that might be Vista x32 or x64 compatible, it might work for Windows 7, but so far, I am not having any luck.
2) Get another AGP card, you would have better luck there with drivers.
3) Replace the MB/processor (but at that point, you are looking at a new system anyways)
Those are currently the only options I can see at this point, but #1 is very least likely.