I've looked at Canon's driver
page for the BJC-250 and unfortunately that model is not supported on windows 7, nor is it supported on Windows Vista. The last driver that Canon released for that model was for Windows XP in 2003 and that definitely won't work on Windows 7.
Canon have evidently decided that the BJC-250 is too old for them to spend money writing new drivers
for it. This is not unusual as other device manufacturers have also done the same with some of their discontinued models.
So if, as you say, you've already downloaded a driver for it I'm puzzled as to where you got it from.
The bottom line is that you'll have to buy a new printer for Windows 7.