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throw all the prx into the seplugins folder.
Now, if this plugin works in the XMB, then open up VSH.txt and add the following line:
ms0:/seplugins/XXX.prx (XXX as in the same name of your prx)
for games, put the same line in GAME.txt
for example, you have aaa.prx and bbb.prx that both are used in the XMB, then open up VSH.txt and put:
ms0:/seplugins/aaa.prx
ms0:/seplugins/bbb.prx
If you have 8 plugins that are used in the same place, then in the txt file there should be 8 lines of :
ms0:/seplugins/XXX.prx