Personally i use FLASH AGENT it is very good and looks quite cool too.
you will need different version of FLASH AGENT depending on your FIRMWARE
for example 3.52 m33-x will need FLASH AGENT D4.
*** ON YOUR COMPUTER ***
download the files you want to flash (obviously =])
Place them on the corret place of your memory stick
(this should bobvious by th file name or should be in the readme)
next- *** ON YOUR PSP ***
run FLASH AGENT
search through the directory and find the file.
press X to select the file.
then click FLASH.
>>>>> however, if the filesize is too big you MAY NOT
be able to flah it, i will be obviou by our PSPs screen
Thankyou for your time. =]