I would start here: http://www.homeloans.va.gov/
Review that information, then, I would contact some banks and credit unions, ask if they participate in the VA Loan program and set up an appointment to discuss with them. As others have said, prepare for that meeting by gathering some of the following information:
1. Your best guess at current mid-score from a credit score perspective.
2. Pay stubs showing income.
3. All of your most recent credit card statements, car loan statements, student loan or other lines of credit (they will use this to look at your debt to income (DTI) ratio.
4. Write up explanations for any negatives you've had over the past several years on your credit report, including collections, charge-offs, late payments, etc. Once you get to the point of applying, you will need to provide this information for an underwriter anyway, so you might as well write it up now.
5. Information on how much you would have available for down payment and/or closing costs.
With that information, they should probably be able to start telling you if you're in the ballpark. In the meantime, do everything you can to try to get the score up. The easiest will be paying off (or paying down) any credit card balances you might have, especially if your utilization is hight on any of them. In addition, if you have late payments, try writing goodwill letters to the creditors to see if they would be willing to remove them.
Good luck!
