PCIe is wonderfully backwards compatible, your PCIe2 card will work just fine in a PCIe1 slot (as long as it is a slot as big or bigger than the card you purchased). It will just run at a slower speed, which is 256MB/s per lane instead of the PCIe2 standard of 512MB/s per lane. In the case of a PCIe1 4x slot it would be 1GB/s which should be faster than a single SSD, but may be a slight bottleneck if you are doing a RAID0 on 2 fast SSDs.
Ok cheers, Looks like I'll use one of the free PCI-e 2 ports then just to make sure theres enough bandwidth. I did read somewhere that PCI-e x4 is capable of around 1000mb/s and that should be enough to the cover the 600mb/s that SATA 3 is capable of, is that correct?
This is the adapter I have
which card exactly do you own?