yah, like bumpin said, just go ahead and replace the whole thing... cheaper in the long run...
of course, assuming that there is a decent sized tear in the boot... if ther is only a slight tear, and is not an old one, you may be able to save the joint, but will require inspection.... basically the problem with just replacing the boot is this... boot rips, you drive around, dirt/debris gets kicked up into the grease, the grease circulates around the bearings in the joint, and the dirt/debris gets inbetween parts and will scratch and mar the surfaces... over time this will lead to a bad joint, sometimes faster than others, so you'll end up paying to have the whole thing replaced anyways.
installation is not too terribly difficult, with the right tools and some smarts...
support car, jack up, remove wheel, loosen/remove retaining nut on end of axle.
loosen retaining nut on end of tierod end (remove key where applicable)
use hammer to tap upwards against nut to free tierod end from spindle assembly.
remove nut and remove tierod end.
loosen ball joint retaining nut (remove key as needed)
use hammer to loosen baljoint from spindle assembly.
remove nut from balljoint
use prybar to remove balljoint from spindle assembly
you should be able to pull hub/strut assebly out away from the axle.
once axle is free from spindle assembly, use prybar to gently pull the axle from the trans.
do not move or jossle car while axle is removed, you do not want to mis-allign the internal parts...
put some trans fluid on end of new axle, and push slowly into trans housing, once most of the way in, push harder until you hear/feel it pop into place.
installation of other parts is reverse of removal....
-hth