When installing Windows 7 it should have installed a generic Windows driver for the sound. All you need to do is go to the Ibm site and enter your model number of your laptop and you can find the drivers there for the sound card.
Also if you go to device manager and you will see the yellow triangle at the sound device so if you right click on it and select properties you can under the drivers tab select update driver and get the driver that way.
If you don't see a Windows 7 audio driver listed on that site above, do not fear! Install the Thinkvantage System Update and it should find you a driver, if there is one. If not, then you may need to back down to Windows Vista/XP.