Sluggish windows are a common problem on lots of cars. To fix the problem, you'll need to remove the door panel, and vapor barrier to gain access to the window mechanisms. Assuming there is no problem with the motor (and it doesn't sound like there is), you simply need to lubricate the window guides with some graphite, or lithium grease. When reassemblying, make sure that you get a good tight seal back on the vapor barrier. This will help prevent any leaks into the passenger compartment.