strut bar?
 

I am about to purchase the front dinan strut brace for my 4.8. Is this thing hard to install?

I don't think its very difficult to install. Our long lost bro, BreytonX5, who briefly stopped by this morning, has this installed on his X5. Here is his post from long, long ago. :D

All a strut bar does is stiffen up the chassis. With a vehicle as structurally sound as the X5, I really can't see it helping that much.

It helps... I didn't notice as big a diff as I did with my 3-series, but I do still feel the improvement as others have described... especially when changing direction abruptly - like in the middle of an S-turn.
I had Motor Works West install mine (they only charged $45) since they were doing stuff too, so I can't say for sure how easy it is to install. But it looks pretty simple.

Should not be too hard if you are decently handy with some tools.

I had a Stillen Strut Brace installed on my FX. Although it has Sport with the 20's it's an absolute must on the FX. Handling is night and day. It's hard to beleive what such a thin brace has accomplished - World of difference. My X5 is pretty stiff especially with with sport pkg & 132's, but I honestly think that a Strut Bar will make it better still IMHO ;)