If your client has a PAL DVD player manufactured in the last couple years and a multisystem TV (fairly common in Europe) then she can play your NTSC disc just fine. Most PAL players will output NTSC, it just depends on the player.
If this is a disc for a single client and you just want to make sure they can watch it, then ask if they have played NTSC discs before, or send them a test NTSC DVD-R.
If you want to make absolutely sure that anyone with a PAL system will play the disc, you will want to make a PAL disc. You can actually convert your footage from NTSC to PAL using Compressor. I can't vouch for the quality of the results, but it is possible to do.
To burn a PAL disc in DVD Studio Pro, you simply set your Disc properties to PAL (this is true in both DVDSP 1.5 and 2). Setting this means that ALL of the assets on your disc must be PAL -- menus must be 720 x 576 and all video must be PAL.
I have authored several replication runs of NTSC DVDs for an international client who does not have the budget to author & manufacture both NTSC and PAL discs. In the past six months we have heard NO complaints from customers in Europe about playing NTSC discs on their PAL players.
Hope this helps,
Jeff