GameShark from
PSP-Hacks forums has released a customized version of the 1.5 firmware which allows you to take advantage of the new media codecs (AVC) available in 2.0. It is run through MPH’s Firmware Launcher. UMD games requiring 2.0 still do not run through this customized firmware, but it's always possible in a future release.
What makes this so special is that when you launch the custom firmware, you can still run all homebrew applications, since it IS the 1.5 firmware, but it also has AVC embedded, which makes it one heck of a nice 'loadable' firmware.
Download it from PSP-Hacks.com
here.