Hey there, oliver williams!
I'd suggest to make sure you have the SSD plugged in the first available SATA port on your motherboard, then install the OS with the SSD plugged ALONE. Once the OS installation is completed, then plug the HDD right next to the SSD. Before doing that, configure the SATA mode of the SSD to AHCI, instead of IDE.
I'd also recommend you a couple of links, that you can use as tutorials:
http://www.overclock.net/t/1156654/seans-windows-7-install-optimization-guide-for-ssds-hdds
http://www.overclock.net/t/664738/how-to-setup-ssd-boot-drive-with-secondary-hard-disc-optimization
Hope this helps!
SuperSoph_WD