The standard mode is 80x25. The mode is set either in the kernel or,more commonly, by passing kernel options in the boot loader. For lilo that's done in the "vga=mode" line. If "mode" is set to "normal" you get 80x25. I'm not sure what you need to set it to for more characters across, but it's a place to start looking anyway. There's also an excellent program called SVGATextMode which comes with Debian, Mandrake and Suse. The source code is available here:
You can set up text modes with this program that aren't available any other way and you can change the text mode without rebooting. Using this program overrides any options set in the kernel or by passing options to the kernel.
Read the documentation carefully on this program. Your essentially changing the resolution in text mode to get the display you want. Part of the configuration for the program is setting up the HorizSync and VertRefresh rates for your monitor and doing this improperly can damage your monitor. Also, improperly setting options in the program can yield a garbled display or no display at all.