ive just aquired my first saab (free), 1985 900. it sat under a tree for a couple of years and i cant turn the ignition key to see if it even runs. the owner says it did. is replacing the switch necessary, and doable for someone of medium technical skills?

A possible solution: I had a similar problem with my first 900 (82). Normally the ignition key can't be removed unless reverse gear is engaged (I didn't know this at the time). I'd somehow managed to remove the key whilst the car was in neutral. I could get the key back in but it would not turn.
So try engaging reverse whilst you're turning the key (with your foot on the clutch obviously ;-).

its an auto transmission, but any similar remedys would be greatly appreciated.

I have experienced this problem. Due to the position of the key cylinder it is possible for dirt, dust and in my case, tobacco from a broken cigarette, to enter into the cylinder. A very powerful vacuum cleaner resolved it! Also, keys do get worn with use. It could be that you may need to get a new key cut. Hope these suggestions work.