clean the boots and throw some RTV over the cracks for now. That will help keep more debris from getting in.
Those boots do rip from time to time...esp with age. More than likely it wasn't due to off roading your truck....unless you were running through chunks of mud/ ice. That'll do it.
Go on ebay and search tierod or balljoint. You'll find full kits on there for cheap. They are not OEM, but a cheap alternative.
http://cgi.ebay.com/ebaymotors/Upper-Lower-Ball-Joint-Joints-Tie-Rod-Idler-Pitman-Arm-/220701077935?pt=Motors_Car_Truck_Parts_Accessories &fits=Model%3AH2%7CMake%3AHummer&hash=item3362cf31 af
However, I prefer using Moog replacments. They are tougher than OEM IMO.
http://www.autopartswarehouse.com/details/QQHummerQQH2QQMoogQQBall_JointQQ20032008QQMOK6693. html
BTW, once those boots rip, those joint are ticking timebombs to fail. It could be a day, it could be a year. It really depends how much crap got in there.