crt tv as monitor:
yes they can be used as a monitor, however, it will look like ***. i've done it in the past just to see if it was possible and although everything displayed as it should the low resolution was not practical. if i rememeber correctly old crt televisions are 480p. this is half the resolution of even the old old 800x600 crt monitors we used to have.
can i connect:
you need either a video card or the motherboard in your old rig needs integrated video. without one or the other there is no component inside to actually produce the video signal. as far as exporting the signal...yes you can most likely export vga to rca. i think this is how i ended up trying it one time but i cannot quite remember as it was a long time ago.
make sure you mean CRT TV as in a television you bought for watching cable, movies, television and not a CRT MONITOR which was bought for using with a computer. while using similar display methods a crt monitor has vastly superior resolution to a television.