For a small office like that, I would take a look at Small Business Server 2003 from Microsoft. It contains a version of Server2003, Exchange2003 plus other bits - it also uses a bunch of wizards to handhold you through the setup, and is quite easy to use if you're reasonably IT aware. This would kill 2 birds with one stone, and any modern server will be able to handle both file/print and e-mail for that number of users with no problems.
 
I would consider putting some kind of firewall in between the 2Meg connection and the wireless router - if you've got an old unused PC lying around somewhere, you could use this to install SmoothWall, which again is quite easy to setup.
 
Shared drives are easy to setup - but make sure that you drum into your users that they only save stuff to the server - not to their local hard drives. This way, you can set up a backup strategy (you had thought about that as well, right?) that only backs up files on the server - keep a Ghost disk handy for when people have problems with their desktops.
 
Again, roaming profiles are easy, but be aware that they can take up a lot of space - and need free space as well (the rule of thumb is that the server needs twice the size of the profile free for each user). I wouldn't recommend roaming profiles for the laptop user, if only because the profile will be sent down the wire each time they dial up (assuming they log on using dial up). If they dial up after logging on, that should be OK.
 
Hope this helps - any more questions, just ask - that's what we're here for
 
Rgds
AndyF