I have a spare Windows 2000 professional machine which I would like to
use as a print server for our mixed Win98 / XP network to take the
load off our rather overworked and underpowered Win2003 server
machine. I believe that Win2kPro is supposed to have a limit of 10
concurrent inbound connections. What I can't seem to find out is what
actually constitutes a concurrent connection in terms of printers.
Does it mean that only 10 computers can actually send a print job to
the print server at any one time, or is a computer that uses the
shared printer considered to be connected all the time that that machine is
turned on, regardless of whether it is actually printing or not?

You must read this Article: http://support.microsoft.com/kb/122920/EN-US/

Pay attention to the description of parameter (AutoDisconnect):
net config server /autodisconnect:time_before_autodisconnect

you donīt have any problem whidt windows 2000 for it.
only when 10 users are connected sending a document for print you canīt connect.
but normally, 1 user send a document for print in 1 or 2 seconds, then
in this moment other user can connect.
the limit is for ten users in same moment.

10 shares is the limit. Use an HP JetDirect print server to provide
unlimited shared. An 11th user will be rejected until an existing user
either disconnects or logs out.