I bought a Nine Hundred just before christmas and I'm planning to customize it this week.

So far from my planning stage, I've only got a couple of tips to contribute...

1) Place black window screen mesh (bug screen) behind the front slots - in front of the intake fans - to help reduce dust. The material is very cheap and you can get it in fiberglass or aluminum.
2) Look in the plumbing section for some nice round rubber flanges. I found some which are perfect for inserting into cable routing holes. You don't want to leave bare metal around the rim of the hole, because it can easily cut into your cables and cause a short.

Steve