Most linux install routines do indeed provide access to a partitioner, but none of them i've ever heard of allow partition resizing.
Partiton Magic is your best bet - you should shrink the current partition and leave however much space you want for linux unpartitioned. The linux installer will probably walk you through partitioning the unpartitioned space. XFS is a good filesystem to choose if you have the option.
Note that partition resizing is a potentially dodgy soulution which leaves some parts of the FAT filesystem out of sync. This may result in slow access to some files, or incorrect free space reports.
Ideally, you would unpartition the drive entirely, and recreate the windows partition but smaller - however, you'd lose everything on the drive in the process so only do it if you have some way to back it up.