Where can I get a PSP downgrade?

First the bad news: no, as far as I am aware, there's no legitimate method of backing up a firmware version, whether you're going from 1.3 to 1.5 or 1.5 to 2.0. I'm sure that's deliberate on Sony's part with the PSP, but in general, no you can't do that.

Now the really bad news: there are some sites that are claiming that they have firmware 1.5 downgrades you can run on your Sony PSP and have it magically go back from firmware 2.0 to firmware 1.5.

Do Not Run Sony PSP Firmware Downgraders!

In fact, they're cleverly disguised trojan horses, programs that are actually written to destroy your PSP unit. If you run one of these downgrade applications, it'll actually remove some key files from your PSP and render it inoperable, which would definitely ruin your day.

As far as I have read, there's also no way to send your PSP to Sony or otherwise have someone clone their OS onto your system as a recovery mechanism (though theoretically you should be able to accomplish this task with some simple programming). If you run this trojan, known in antivirus circles as Trojan.PSPBrick, you'll have a dead, throw it away, nothing you can do to fix it Sony PSP unit.

Quoting from a ZDnet article on this subject: "Basically the (PSP) is completely inoperable, and you've lost your device," said Eric Chien, the principal software engineer at Symantec Security Response. "It's called 'bricking.'"

If you've upgraded to the 2.0 firmware release, I am afraid that you're stuck with it. Just don't get stung by this trojan while trying to fix your unit.

Update: To be fair, I have heard from a number of PSP owners that they have successfully downgraded their PSP firmware, from 2.6 back to 1.5, 2.5 back to 1.5, and so on. I imagine you could flip a coin and hope that a given PSP firmware site has a legit and trustworthy downgrader that you can run on your Sony PSP with good results, but to me this is still a pretty risky move because while the odds of success might be pretty good, the cost of failure is pretty darn high too.

As with anything to do with computing, you need to decide for yourself. If you can find a credible, trustworthy site and believe the postings from other folk that they've had success with the downgrade, go ahead and try it. Whether you succeed or fail, please do pop back here and let us know too, but, again, how will we know your posting is legit, not a trick intended to get others to download a "brick" application?

Round and round. You can see the basic dilemma here.

Good luck, whatever you choose to do.