I'm having exactly the same problem trying to get Windows 7 to access my Brother HL-5050 which is on an XP computer on my local network.
The problem seems to be that Windows 7 fails to understand what kind of printer it is trying to find a driver
for and ends up searching itself and Windows Update looking for a driver for "unknown" printer
I have manually loaded the correct driver, but Windows 7 refuses to use it because it says it isn't the correct driver for the unknown printer
When the &*^$%^&$%&^ folks at Microsoft decided to make Windows 7 "easier" to use, they removed the capability to manually tell the operating system which printer driver to use.