Nokia N900 gets disassembled on video, all you need is a philips screwdriver, Torx 6 screwdriver.
Step-by-step video disassembly of N900.
Keep in mind that this video is unofficial and we suggest to don’t try on your own, because you can damage your N900. ;)
There are also picture step-by-step disassembly at Nokia Service Manual for N900. You can downlaod it from here (PDF, 1,78MB).