The prxes we build are strange IDA doesn't really like them, for Sony stuff grab prxtool from subversion and do prxtool -o newfile.prx -e sonyfile.prx to be able to load it in ida. Whether that works for our stuff I couldn't say :)
PSPDEV tools and libraries can be found in the psp/ repository at
svn://svn.pspdev.org/. PSP homebrew games, demos, and other applications
can be found in the pspware/ repository located at the same URL. To view
the contents of these repositories using a Web browser, visit http://svn.pspdev.org/.
There's even more in the readme about it. Perhaps taking a moment to read it over could avoid the embarassing question you just asked.
Or you could just change two bytes at 0x10 of the file to 02 00 and IDA will load it fine. Select mipsl mode for processor type.
The more useful thing about prxtool is that you can get it to produce an idc script that will do a lot of organisational work for you once you have an elf disassembled.
Is it within our legal right to disassemble and analyse boot.bin files ? I ask this first, before asking why IDA doesn't seem to disassemble them properly...