We had already created our Thinstation image so we had all the thinstation files that we required. Instead of going into the ISO folder (for CDs) go into the PXE folder and save all the files in the folder for later. (Let me know if you need more information about this)
Here is how we did it!
1. Install a TFTP server from TFTPD32
Make the settings look as follow
The folderlocation should look as below.

Two extra [server options] need to be added in the DHCP console.
067 is the relative path to the thinstation pxe boot files. (I created a thinstation folder in my TFTP directory but this is optional).
3. Configure the bios on the PC thin clients to boot from the network with PXE.
Hope this helps someone