In his remarks at the Tokyo Game Show, Sony Entertainment President Kaz Hirai said that the PlayStation Store will be available on PC, as well as on the PlayStation. This means that you'll be able to do things like download games for the PSP without dropping the cash on a PlayStation 3.
The service, which is already live in Japan, should be coming to the States in the not-too-distant future. You can go to the website now, but you're going to have to navigate it in Japanese. Of course, if you can do that, you're kind of a stud, so we're rooting for you.