If I know my jeans size, for instance 32", 32", can I convert this into an estimate for standover height on a bike?
This might not be a very good place to start from when sizing a bicycle. Your inseam measurement is from the top of the crotch (top inseam point) to the BOTTOM SIDE OF THE ANKLE (lowest inseam point). Your feet go all the way to the floor.
Inseam is specifically to determine what pants you wear. I might point out that pants and bicycles are made and sized quite differently.
As @darkcanuck suggested, you're better served to stop by a local bike shop (LBS) and have them size you. Most LBS sales people will be more than happy to put you on a couple of bikes and let you take a test ride, even if you say, "I don't plan to buy anything today, I'm just starting to shop around." It won't cost you anything and you'll start to get a feel for how different styles of bikes feel in different sizes.
Note also that standover is not the only measure you need to size your bike. The TOP TUBE length will also come into play--depending on how long your arms and torso are. Different manufacturers build different bikes with different ratios of top-tube-to-stand-over.
Depending on the bike, you will also want to consider handle-bar width, crank-arm length, etc. Don't plan to buy a bike off of the internet because it has the right stand-over! At least, don't be surprised if you do so and then it doesn't feel right.
Try out several actual bikes--even if they aren't ones you plan to actually buy--so you know how those different geometries feel when you're riding.
AND IF YOU'RE LOOKING AT A USED BIKE... it still pays to try out some new ones and know what geometry suits you. When you are negotiating with a seller of a used bike, show up with tape measure in hand!
The short answer is no. For information on frame sizes and all things bikes, consult the late Sheldon Brown's website: http://www.sheldonbrown.com/frame-sizing.html
It's an incredible resource!
It's close enough for a very rough guess, but in most cases (especially if using a sizing formula) you'll want to measure the distance from the ground right up to your pubic bone. Unless your pants drag along the ground, you're inseam size will be a bit shorter: somewhere in the range of 1-3" (as a guess).
You can get this quickly measured at many road bike shops as part of the shopping process (i.e. it should be free).