Can people get your personal information if you sell your PSP online? How do u clear personal info off a PSP?

I never played online and only used the memory stick. Also, this PSP was won at an auction and does not have a bill of sale and is not registered.

Can anyone get personal info. off my PSP if I sell it without the memory stick?

How do I delete any remaining information on the PSP itself?
(my user name, account info, game statistics, etc)

Your replies are much appreciated, cuz I need to know SOON.

Thanks everyone and have a nice nite/day (for which ever timezone u are in, lol).