I've run serial mouse, keyboard and monitor cables 50 ft. before. That is the max distance for the RS232 spec though, so I'm not sure how much further it could have gone, but it worked fine at that distance. Remember though, your milage may vary based on your hardware and the quality of your cables.
25ft aye?...I can test it tonight when i get home. I know I have atleast 22ft...Im sure I can scrounge up another 3. You setting up a home entertainment system or something? We are taking about the 15 pin cables right and not composite video (the yellow ones)
I'm a ghost...email me if you have any questions on my old setup