A few things spring to mind:
A lot of applications / services automatically started by Windows. Especially if there is any AV / spyware / disk checker etc. running at startup.
The computer tries to connect to a resource on a network-connected PC that is not responding.
The user profile that is logging on has grown very large.
A peripheral device is slow to respond.
I'm not sure what effect fast-user switching has, if you have a lot of users sharing the PC (I use XP pro), as presumably the OS has to load all user profiles? I may well be wrong about that.
Free space and fragmentation of your hard disk (and pagefile) may also be a contibutory factor, as is the amount of RAM. If you have a lot of programs auto-loading, the system may well be paging them out to disk before you actually get to use it! 256 MB is not a lot these days - a further 256 should only cost about £50.
Some food for thought.
No idea about the printer.