That all depends on where it is loose... If it is the flex plate to torque converter, it should be as simple as supporting the car on jack stands, removing the dust cover and tightening the bolts down with a wrench.
But, if it is the crank to flex plate bolts, then you may have to pull the transmission just to get at them... You may not have to actually pull the transmission, but you will need to unbolt it from the motor and move it back atleast an inch to gain access to the crank to flex plate bolts.
I would try to tighten the TC to flex plate bolts first, then if you don't solve the problem, move on to the extreme of pulling the Tranny.
1994 Intrepid ES - 3.5L w/ 167k miles - SOLD 04/01/04 for $2200 - Man do I miss it!