Fundamentally, that is an issue you have to take up with Sony - As they would need to provide the proper chipset drivers if/since Win 7 didn't automatically identify and install them for you. Being the corporation they are, at this juncture, the expected answer from Sony would be along the lines of "Thank You for purchasing your Sony... we cannot support Windows 7... we haven't and won't test it on your older device... but we are working hard to provide the finest available when Win 7 is completed... we look forward to your purchase of a new Sony laptop with Windows 7 in October...
But if(when?) they're not helpful, the steps you would need to take are to first identify the exact chipset - Services like http://www.idhw.com/
can be helpful in accomplishing this. Once you have that, you can go to the original manufacturer of the chipset (Intel, AMD, nVidia, Via) and see is an available generic version of the proper driver.
Be advised that could potentially cause other issues if Sony had to write some proprietary drivers for their hardware.