Did you run the Windows 7 Upgrade Advisor
to get a heads-up on any issues?
I don't see a Vista Display driver on the Sony Support Downloads webpage for your model. The Intel Chipset 82852/82855 Display drivers do not support anything later than XP, although you can try the Intel XP driver as well to see if you get better resolution.
You can also try running these XP drivers' extracted files .exe in XP Compatibility Mode
Did you get a newer Display driver via optional Windows Updates? This is how Windows 7 updates its drivers from those given by the installer.
Let us know the exact Display device and the driver versions you have tried. We can help you find another driver to try.