XP already knows the 1100. Otherwise, you just download the HP executable and run it. It creates a folder which you can alter. You find your printer and do a right click. Go to Properties/Advanced. Click on "Update Driver". From there you will navigate to the folder created in the previous step. It may have subfolders to accommodate other languages. You may also need to decide which PCL level (5 or 6) you want. Stay with the one you have now if it's working. Hope that helps.
I've found a couple of driver upgrades for my printers on the HP sie but no info on how to implement them. (HP 1100A and 2000c).