Yep you sure can - PS1 emulation will not be leaving the
PSP. The problem stems from different games working better with different versions of POPS.
So yes, you will need popsloader to get some games working the best they can (and sometimes so they don't freeze).
Dark-AleX - PSP Developer is what you're after for the latest version of popsloader.
The games go in /
PSP/GAME/(gamefolder)
eg. /
PSP/GAME/FF7
I can post up all the version of POPS with popsloader if wanted... all you need to do is copy to your memstick and activate the plugin in recovery.