I had these lamp guards on my D90 but had to take them off because of the installation of the safari roof rack... Are these what you mean ?
Or the smaller one's that everyone has ?
For these all I had to do was drill a couple of holes in the body (which sucks now) and it took maybe 30 minutes total on the install. It's a piece of cake. And I've seen the installation for the smaller one's and it's even easier.
Hope this helps.
<EDIT / ADDITION>
If you're buying them new they'll come with all the necessary hardware but if they're used you may have to come up with the bolts.
AND I forgot to say that mine had these little 'tubes' that you installed through the body and that's where 2 of the bolts went on each side... so they could 'swing' open... for cleaning and such.