Sony will release a new PSP firmware update today that will let you window-shop in the PlayStation Store without a PSN account.
Version 5.50 allows all content - games, trailers, demos - to be browsed. It also lets PSP users view the PSN Information Board, providing you have a Wi-Fi connection.
This can be seen on the XMB menu and keeps track of the various PlayStation Store offers.
And that's it; no motorbikes or anything.