Changing instrument cluster need help

I just bought a 91 GMC Sierra and it has a guage pannel like this,
http://imageserver.carsoup.com/1GCDK/1GCDK14K5KE251180-5.jpg?xt=56962
and I want to put one like this in it. How would I go about changing it , also how would I hook up the tachometer.
http://chevytruckworld.tenmagazines.com/gallery/88GMCtruck/232055.jpg

I know that it is a gmc but is almost exacly the same as a chevy.

I don't know for sure given you have two different style guages.... your orginial guage is that "quasi-digital" type and the type you want to replace is the old school analog.
if if give yous you any help.... I have a 92 k1500 that had the regular guage cluster without the tach.... I found another cluster with the tach and repacled it. Simple bolt repaclement, no modifications or changes, and the tach works. On that year truck the cluster just connects with one uniform blade type connection. Truck has tack wiring as part of teh stock harness.

I would be that you might be able to just unplug your old cluster and install the new one. THe catch with your pictures is that you have two different styple guages?