ya I think I'll just format the whole 8GB SD card as one partition as I've got OS3.9 with all the updates and I've already got a 'real' scsi drive plus and IDE CD too so this is just more storage.
That will *not* work, not with 3.9 at least. The problem is the following: The ROM FFS and the ROM scsi.device will not be able to address any byte beyond the 4GB barrier, and hence will not be able to boot up your system, and hence will not be able to load the patches to actually *get* access to the additional space.
Chicken and egg problem.
You need a small boot partition that contains at least the ROM-Updates (or equivalent, e.g. scsi.device in DEVS:) and SetPatch (or equivalent, e.g. LoadModule), boot from there, and *then* once the system is booted, you will see the remaining partitions just fine.
Also, please make sure that you place the v45 FFS in the rigit disk block (HDToolbox can do that for you), otherwise the system will even attempt to mount your second partition with the old FFS, and will by that invalidate data on your first partition (outch!).