The problem is: my desk is small, so the TV and the PC monitor must be close one to the other. When I turn on both, at the same time, the PC monitor´s image changes (shakes a little and black moving lines appear), as it´s being under some kind of interference. Is there any solution to this, like an isolation material to put between the monitors, to stop the interference? Or should I build another desk and put the TV monitor there, far from his enemy?

A classic problem. It can happen with any type of machinery: a fan, a sound machine, television...
As far as I know the only solution is to move the television. Some material might work, but I am not sure what kind...

Maybe not what you had in mind, but you might consider replacing either the TV or computer monitor with an LCD panel. That would let you keep everything close together.

1- I thought it might help if you set your CRT's refresh rate to 60Hz, but that would cause eye strain.

You can change the refresh rate by right-clicking your desktop --> properties --> settings --> advanced --> monitor (something like that).

2- Putting some steel between the two monitors might help... I tried it myself with CRTs but it didn't really help me.

There's some expensive material that does this, but you might as well get some new furniture or a new LCD.

Thank you guys. I guess I´ll move the TV. LCD is completely out of my budget now.