Had same problem with my Canon BJC250, not only print jobs stacked up
in que, but printer output was gibberish, smudgy lines from time to
time. Printing one page at a time or restarting print spooler was
only a temporary fix.. It is due, I think, to the way Windows XP
shares resources by software.

Found a solution, so far so good: Go into the BIOS and change the
parallel output setting to "ECP & EPP". Do not use "bi-directional".