Group Captain Smudger

I have a 93 Kona Lava Dome that is in serious need of some upgrades ('bout time you might say). I've lost touch with the latest "must-haves" so I'm a bit confused concerning replacing the original chainset (cranks, rings). The Truvativ 5D-A1 looks good but mentions 64/104mm BCD. What's this? The FSA Alpha Drive specifies an ISIS spline. Hey? And are chainrings really "speed" sensitive, i.e. can you not use a 9sp chainring with a 7sp cassette?