|this can be done BUT you'll have to do a fresh OS installation. Once the physical disks are configured into their virtual volumes, you can install your OS. non-system volumes can be deleted and resized from within Windows, but not the system partition (usually C:).|
Also: most will recommend against Raid 0, ESPECIALLY for your system partition. if either disk dies, the whole volume is lost.
with SSD, i doubt you'd need the performance gains that Raid 0 is typically used for.
I would either a) use the 2 80G SSDs in a RAID1 mirror, for data protection, or b) just put the OS on one and use the other 80G and the 300G for storage. You could make 2 virtual partitions or even span them both and create a single virtual 380G storage partition.