Cuerno is the main and dominating peak in the north seen from Aconcagua's western base camp Plaza de Mulas. Walk straight towards the peak and negotiate your way around steepest sections of the glacier ridges. There is a small rocky peak in the middle of the glacier. Be sure to walk on the right hand side of this one. When you have passed this peak and have Cuerno's massive south face in front of you the climbing starts.
There is one crevasse on the route. It's at most places a horizontal one, but on the eastern end of the south wall of Cuerno it's running down the wall vertically.
Climb up gently angled snow. It's your choice how high on the wall underneath Cuerno's face you wanna go. The higher you go the steeper. You'll have to check to your right where the most plausible place to cross the crevasse is located.
Traverse to your right on 35-45 degree snow/ice. Be careful as there are places where the snow layer is very thin and blue ice is lurking underneath.
When you are underneath the lowest point (roughly) of the ridge, you will have to decide where to cross the crevasse. In early 2005 it was not a wide at its narrowest point and the crossing was easy.
After the crossing the climbing starts for real.
The slope gets gradually steeper and at its steepest parts it'll be close to 60 degrees. This will continue to the ridge and the distance since you crossed the crevasse is approximately a 100 vertical meters. The ridge may be corniched.
When on the ridge, you can basically walk up to the summit of Cuerno. The closer to the south face you go, the steeper the climb up the eastern slopes. The summit is rocky and be careful with loose rocks.
An experienced ice/snow climber is probably content in attacking the peak with crampons and two axes.
You can climb down the same way you ascended without any additional gear.
For those who wanna play it safe or don't have so much experience on ice and snow, it's probably good to bring a snow stake or two, possibly some long ice-screws, rope and personal gear (harness and a rapelling device). A helmet could be of use as there are smaller pieces of ice bouncing down the face now and then.