Can I share my external hard drive from Windows machine to Mac?

I have a Windows desktop and just purchased a Macbook Pro. I'm trying to use my external hard drive to back up files on my Windows and Mac computers. I have the external hard drive set up with 2 partitions. One as FAT32 and the other as HFS+. Is it possible to leave the external hard drive connected to the Windows computer and also be able to use the HFS+ partition to use with Time Machine for my Mac over my network?