Sharing single instance of iTunes with iPad and iPhone
If your iTunes library is small enough to fit completely on each device, then yes, you can manage and sync both devices to the same PC through iTunes on that PC and a sync cable.  You can even create separate playlists in iTunes on your PC and sync a specific playlist to each different device.

Another option that you would want if your music library is larger than your devices, is to invest in an "iTunes" Match subscription with Apple:

http://www.apple.com/itunes/itunes-match/

Then, your entire music library from your PC will be available from the Apple "Cloud" and can be streamed to any of your iOS devices.

Just make sure that your PC, iPhone, and iPad are all logged into the iTunes Store using the same AppleID and you should not have any problems.