You have to go through a bank - same as with a regular mortgage. They do a credit check and require the same information as if it was a conventional mortgage. They are a bit more forgiving on credit issues and also allow you to borrow a higher percentage of your income (most banks go with 30%, but with a VA loan, it could go as high as 45%).
A lot of sellers don't like to sell to people using VA loans because they are responsible for some of the closing costs (they will usually increase the price of the house to make this up in the end) and the VA can be REALLY picky about inspections and make the seller fix silly problems.
If you are going to use it, start the paperwork process now. It took many months to get the paperwork in for us and, in fact, they didn't send it in time for us to close and we had to re-work our entire loan.
Our limit was $250,000, but I think it varies depending on where you buy and what the housing market is in your area.
Call around and talk to a few lenders who handle VA loans. See what their options are. Maybe it's your best option, maybe not, but a lender is the best person to tell you what the various options are.
Good luck!