Getting Linux to read my Windows shares was a bit of a pain but now I can mount all the drives in my network with a small script. Now I need to work the reverse. I have a FAT32 Partition which I need Linux to share with the Windows machines on the network. Where do I start? This should be easier I hope?

It's completely transparent. The Linux VFAT driver is extremely mature and robust, and usually built in by default. Just mount the partition and have a nice evening!

Linux already has the FAT32 partition mounted.
I need Linux to share that partition over my home network so Windows can see it.

Perhaps look into Samba? I don't know enough about it to give details on how to set it up, but I know it can allow you to have files on linux shared with windows clients through a home network.