I've seen sata -> pata converters but I've never seen pata -> sata. It won't improve speed at all even if there were adapaters. pata is 133MB/s which is much faster than any reasonably priced magnetic drive can reach. So unless you are using SSDs, you aren't going to see a difference if by some low chance you do find a pata -> sata adapter.
If you want a few more sata ports, you should have gotten an ION board .