yes you can and not much. i've never done it personally; but i believe there is a nice write up on the main page. search steering box adjustment or something to that effect on this board as well b/c it's definitely been done by other members here. taking pics and reporting how it went is always appreciated here also.
You can remove the play in the steering box, but any play caused by rod ends etc of course would still be there. Loosen lock but, turn grub 1/8 or 1/4 and retighten lock nut. Start engine, roll down window, stand outside and watch tyres as you slightly turn wheel each direction to check for play. 8-|=
I've done this on a number of trucks, recently an F150 and my Jeep ZJ. I highly recommend you take a scratch awl or simliar and mark the grub and the lock ring so you know exactly where they were when you started (like marking a driveshaft before de-coupling).
Small increments are the way to go here as rrtoadhall said, too much adjustment and you'll bind up the box. Start with a slight turn, check for play and binding, if more is needed keep adjusting but always check for binding as you go.
X2 w/ rr's suggestion about rod ends - this would be a good time to check your suspension joints for slop or loose nuts as well. I've had a trac bar work itself loose on an old XJ and caused fits.