You might want to read the thread "May I ask the masters for advice" on the appropriateness of posting your request on this particular form. I'd suggest perusing the Soils forums for full details, but the short answers to your questions are:
1)concrete is not toxic - it may leave the soil slightly alkaline, but many veggies will prefer a neutral to slightly alkaline soil
2)No
3)a homemade sieve works swell for removing larger rocks - don't sweat the small stuff
4)add quantities of organic matter (compost) and till in well. The soil is likely not infertile - only badly compacted. OM and loosening will help considerably.

Also, I would suggest that your soil be tested prior to adding any ammendments. You can inquire about getting a soil test through your county extension office. Usually costs around $10 and should be well worth it.

Thanks all.

I found more info from our local MG affiliates at
http://mastergardeners.org

Regards,
/venkat