i have a 1993 j30 that i want to get a new set of rims for. i need to know what is the biggest diameter i could go without the rims rubbing on turns or bumps.I also need to know the specs on the lug pattern in mm.do i need special rims because of rear wheel drive?

as a previous owner, you can put 19"s on without any major discomfort. i had 17's (enkei) on it and it was a class act.
I don't recommend anything bigger than 18's though

Here is a link to a handy tire/wheel size calculator: http://www.miata.net/garage/tirecalc.html

You can use this to see what size wheels and tire wall you will need to keep it around the stock size. This calculator will show you how much of a speed difference the car will have and its your call on how big you want to go.

I have a set of 03-04 G35 coupe wheels and am running 225/45-17 in the front and 255/40-17 in the rear.

I have seen people add 22's but i thinking they added a lift kit maybe a 2' .