Unless you installed a new card, check the disks that came with your computer. They should have the driver. Or if you have a copy of Vista, have it search that DVD for the correct driver.
If that doesn't work then -
Go to Device Manager and see if your network card is functioning.
Click the windows icon, type in "Device Manager" and press enter.
Click the arrow by the Network adapters.
If it has a problem with driver it should tell you.
You can right click - properties
Then check if it is working properly and what the current driver is.
You can try replacing that file or take down any info on the type of card and do an online search for drivers of that type of card.