Adam96, are you working with FreeNAS
.7x?
For that version 256MB of RAM probably meets the requirements, but version 8.x (notice the 8
before the dot) published minimum is 6GB, though you can make it work with less with varied results, 256MB is just not enough. There's a link at the top of the page for version .7. With version .7 you can boot from a hard drive, but with 8.x you must use a USB flash disk.
You might need to use a partition manager and make sure the drive you're using for FreeNAS is set to 'active', but then things get a little complicated because you'll need a 'boot manager' so that you can choose to boot Windows when you want. I suggest you look at the other link for .7 at the top of the page and see if you can find more info there.
Here's a link to a boot manager that will help, but I can't go into details on how to use it.
http://neosmart.net/dl.php?id=1