The best way is to upgrade to 3.90m33,download CMXB & put it in root of memory stick.Enable the plugin in recovery,then put your .ctf themes in PSP/Themes folder on your MS.There is no need to flash,there is no way you can brick & you can have as many themes as you want.You can get themes from here
PSP Themes, PSP Customization, PSP XMB, PSP PTF, PSP Wallpapers, Custom PSP Themes, Custom PSP XMB PSP Themes Releases - Console Spot Forums - PSP DS PS3 Xbox 360 Wii XMB
You can get CXMB from here
http://www.consolespot.net/forums/ps...selection.html