You should not do this. Linux is made for Linux file systems and Windows for
Windows file systems. You can always install a utility in Windows to read
ext partitions. I am not sure if they can handle ext4, but ext3 works fine.
See:
www.cyberciti.biz/.../...xt3-ext3-file-system.html
http://www.fs-driver.org/

FAT32 has many problems that you would not want to introduce to Linux. Most
Windows users would not use it, but would use NTFS instead.