Is this a drive that you've installed yourself as an upgrade? If so, you might check your BIOS to make sure that the hard drive controller isn't in "Legacy" or "Compatability", etc mode. If this setting is turned on, it will disable some of the improved performance features supported by modern SATA drives.
You can also try downloading the free Ultimate Boot CD for Windows and running some of the disk benchmark tools from there to see if there's any difference compared to what you're seeing from within Vista.
In addition to benchmarking, you should run some diagnostic tools to see whether the drive is getting a lot of seek errors. Often when drives seem to work fine other than being a bit sluggish, they are actually getting a lot of seek/read errors behind the scenes that are being corrected on the fly by the drive controller's error correction software. Windows seems to have a pretty high tolerance for the latency caused by this, so it will often continue to run for a long time before the problem is corrected, but once a drive starts to get excessive errors it's a good idea to just go ahead and replace it if you can afford to, because it'll just keep getting worse until it fails.