Ouch.
Alright then.
I'm assuming you're using Lilo to boot.
It's actually lilo that passes the framebuffer configuration to the kernel at boot time. You need to find a way to change lilo.conf so that the line that says
vga=normal
instead of vga=746(or some other number)
Rethinking this, I think it might be possible to pass vga=normal at boot time. So, reboot and at the lilo prompt, enter the name of the linux boot selection (mine is labeled with the kernel version)
Should get you into normal vga mode from the lilo boot prompt.
Again, be sure to replace 2.4.22 with whatever label lilo uses for slackware.
That will get rid of the framebuffer console, and you'll be able to log in with ctrl-alt-F1-F6
Another way to do it, if that doesn't work is to use ssh (that's secure shell ) to connect to your box.
If you're on a network, you can either use another linux box:
ssh your.ip.address
or a windows box.
Download PuTTy for windows to ssh from there.
Hope some of this helped
-Shade