Hi-fi speakers do have strong magnets in them. So do speakers which are meant to be used near computers, but they also have magnetic shielding for the reason you have found, namely that CRT monitors can be affected. CRT TVs as well. As for your hard drive and CPU, forget it. They will be fine.
The answer is, keep the speakers far enough away from the monitor so that they do not affect the colours ("colors" in America). Then everything will be fine. Or buy an LCD monitor, then you can put the speakers where you like.
One more thing -- the magnetic field can erase floppy disks. Not CDs or DVDs. So don't store floppy disks on or near the speakers.