A portal is basically a set of webpages that are saved as HTML files to your memory stick. Therefore they open in the PSP's Internet browser, yet run offline. In this example, the pages are styled like Windows Vista, although this particular portal comes with an option to use a Windows XP theme as well. You may be interested to know that not all portals are designed to look like an OS. Some have an original design.
Please note that YOU DO NOT NEED CUSTOM FIRMWARE for this to work. It will work on any PSP software, as long as it has the Internet browser option (system software 2.00 upwards). If you do happen to have custom firmware (as do I) it will work just as well.
Please also note that this is not an official Microsoft product (as you probably will have guessed) , but it is completely legal and will not harm your PSP in any way.
Step 1: What you will need:
1) a PSP (duh!)
2)PSPWVISTA 1.7 http://www.megaupload.com/?d=W65KIHL8