The applications transfer between users unless specificially chosen to not be installed for other users on this computer (When the application is initially installed, and not all have this option)
As for pictures, they were probably imported to the Shared user account. In this, all the Pictures, Music and documents that were saved in this Shared account, are viewable and accessable from all and any account, even new ones.
To remove them from the shared account you have to go into the account folder.
XP:
My Computer: "C:\Documents and Settings\All Users" In here, check the folders for any data/pictures that are in there and remove them. Check all viewable folders.
Windows Vista/7:
My Computer: "C:\Users\Public" Same as the XP one, check all folders for any data.
If there's data in there, remove it, and check into the new user's folder's to see if they are there.
As for applications, you must go into Add/Remove Programs (XP) -- Programs and Features(Vista/7) and remove the applications yourself.
**Updated: If you feel safer reformating and reinstalling windows, and all you are worried about is drivers, the best option would be to download all the drivers for the computer BEFORE you do the format. Save all these drivers to a CD/DVD/USB Flash stick, or External Hard drive, something that you can use after the installation, however, if you are worried about not getting all of the correct drivers then it'll be a bit more complicated, but no impossible**