Brewology

Ok first off there are easyer way to do this first try to decompress your PRX with 'prxdecrypter'
if it tells you something like i donno...
Decrypting VSHMAIN.PRX -> Output unexpected -> Failed to decrypt -> Deleted

so if the first part didnt work you can still do this...
1.) Open the PRX with a HexEditor i use HDD Hex Editor
2.) Select only the data from (offset)0x150 till the end of the file
3.) Save the selected data as "filename.gz"
4.) Open and extract the *.gz-archive with 7-Zip or WinRAR and rename it to "filename.prx"

now you have the decompressed(decrypted) PRX

Wow!
Nice tutorial!
Great for just decompressing one instead of using a program that requires all of them to work.