Yes, the motherboard or SSD will scale down to meet the needs.
SATA II are going to be hard to find, and no cheaper than SATA III.
30GB is going to be hard to find, start with 60-64GB.
My recommendations, without a budget are: Intel 520 60GB, OCZ Vertex 3 60GB, Samsung 830 64GB, Mushkin Enhanced Chronos 60GB.
Follow Dereck47 advice, and use the SSD cache option of the Z68 chipset.