Well,
1.) Search for a plugin wich is compatible for ur type of FW
2.) When u hv d/loaded the plugin, u will always get sum folders in the plugin, out of wich ONE OF THE folders WILL always be named as "seplugins"
3.) copy all the contents(all the FOLDERS) of the plugin into ur PSP's root i.e the place in the mem stick where there are folders like PSP, ISO etc etc..
4.) then boot ur PSP in recovery mode (switch OFF the PSP after transferring the plugin folders in the root of the PSP and switch it ON by pressing the R trigger and then Sliding the ON button)
5.) once in the recovery mode, scroll down to >Plugins and there u will see an entry named as <your_plugin_name>.vsh and the status of this plugin will be <disabled> coz u (for the obvious reason) hv not yet enabled the plugin (silly me..lol..
)
6.) select the plugin entry adn press X on ur PSP, to enable the plugin, EXIT out of the the menu and out of the recovery mode and let ur psp restart in normal mode..
7.) depending on the type of plugin u hv installed and enabled, it will vbe activated on ur PSP (read the readme provided with the plugin tat u hv d/loaded) for more instructions..
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Hope my explaination didnt suck !! lol..