Yes, the Dvorak is heaven. You can set it in Windows XP in the control panel regional and language options.
I switched over to dvorak in Februrary '05. To really do this successfully, though, you have to completly change. I had to switch my home PC, laptop (that's fun because some of the right hand side keys are smaller, like the semicolon which is now "s"), and work PC. There was a learning curve of about 3 months, and I probably use a PC atleast 3 hours a day, everyday.
For anyone who really thinks QWERTY is just stupid, dvorak makes a lot of sense. Putting all the vowels on your left hand, in the "home row," makes typing much quicker, even though I could type about 60-70 WPM in QWERTY. Though I haven't tested myself recently, I was doing about 75-80 WPM in dvorak last year, so I'm probably capable of 80+ now.
So there could be a speed increase for some slower QWERTY typists, but the best benefit I've found is that, like you said, you can type more words on the home row. What this actually means in practice though, is that you don't have to move your fingers as far to type something, so you can type more without having your fingers hurt.
Tom's had an article, probably back in '04, about dvorak keyboards. I tried it then, but didn't want to spend time adapting. I'm glad I did.
Here's a real bonus: very few people can type in dvorak, so if you setup your PC to only use dvorak, nobody can use it but you
There's some real security. I had IT ask me "what language is that keyboard in?"... I replied, appropriately, "English."