Please post the model number of the Vantec SATA 2 PCIe card so more detailed information can be provided.
Modern 3rd generation solid state drives require 4 channels as in PCIe 2.0 x4 (or PCIe 3.0 x4 ) for optimal performance. There are low budget and entry level SATA cards that have just 2 channels. In addition there are some cards that have 4 channels but as soon as a second device is connected the channels are split so each device has only 2 channels.
That's alright, I'm ancient too, and so is my computer. The Vantec card model # is: UGT-ST300.
now I'm wondering if my mobo is
There may be a boot problem too. It is not always possible to use a drive connected to a card as a boot device. Whether or not the drive can be used as a primary boot drive depends on the motherboard's system BIOS. There may or may not be BIOS settings for such a configuration.
If you have a motherboard that supports solid state drives and an unused SATA port on the motherboard, then you would be better off connecting the ssd to the SATA port on the motherboard. That would eliminate most of the problems associated with add-on cards.
SATA 3 6Gb/s ssd's are backwards compatible with SATA 2 3Gb/s. However, the ssd performance will be restricted to SATA 2 levels. Typically a consumer would not notice the difference between SATA 2 and SATA 3 performance. One would have to run synthetic benchmarks designed to grossly exaggerate minor difference in order to measure them. It would be different if the user was a rocket scientist or a Hollywood film editor.
EDIT - I think I made a mistake and got things mixed up. It is very easy to get confused at my age. It is supposed to be PCIe x2 for standard ssd's and PCIe x4 for PCIe ssd's.
In the meantime while checking for new hardware reviews a little while ago I found a review over at Maximum PC for a fairly new PCIe adapter card designed expressly for ssd's. It will also let the ssd function as the primary boot drive. It looks promising. Here is the link:
http://www.maximumpc.com/article/%5Bprimary-term%5D/apricorn_velocity_solo_x2_pcie_ssd_adapter_review
NOTE - You'll have to check the system requirements.