Sony Japan has released a Japanese PSP demo version of Mercury Meltdown along with new firmware for its shiny handheld.
The 2.8 firmware adds RSS video support, amongst other things, and should work on your system whichever region it's from - although US and European versions of the downloadable should be made available shortly if you're anxious about it.
Meanwhile, the Mercury Meltdown demo can be downloaded either direct to your PSP or through your PC.
If you're planning to do the latter, you'll need to drop the file in a "/PSP/GAME/UCJS10043" directory on your Memory Stick.
We'll let you know when the 2.8 firmware's available from Sony's US and European sites. Reports earlier this week suggested there'd be a World Tour Soccer 2 demo at the same time, so we'll let you know about that, and any news on an English Mercury Meltdown demo, soon.