I'm not all that keen on the tents etc. I do have a small table that I use as a platform for some more 'studio' type macro
Backgrounds generally aren't necessary when I'm dealing with small critters either (unless I want to add some greenery close behind them). Even with a white wall 6ft away from you, if all your flash power is directed onto the subject, then the background will turn out black.
To hold things, I recommend going to Jaycar, and buying yourself one of these.
PCB Holder with Magnifying Glass - Jaycar Electronics
Throw away your magnifying glass and you have a perfect setup to hold onto things. I'd use this for a lot of my studio jumping spider shots.
When you're dealing with macro, the most important thing is light, and you'll need lots of it. When you shoot at 1:1 and at f/20, you can't really use natural light.
A lot of the problem with getting light onto your subject will be flash positioning, especially if you choose to use extension tubes, where you'll lose even more light. Rigging some aluminium together, and gutting a tripod collar, and then adding a ball head, you can make yourself a flash bracket.
If you're not using tubes, then you probably won't have to go to this extreme, but it IS a handy bracket if you ever want to try to do night time macro and need some extra light to focus.
Being that you have the D90, you can save money on triggers and just trigger external flashes with the popup flash on the D90 in commander mode.
I'll post a little more tomorrow, but I'm knackered now and desperately need sleep. hehe.