what version of mandrake are you using? that helps us out when we are trying to solve a problem.
this is what i would try. if mdk (mandrake) has your monitor, but not the graphics card, you could put in a generic vesa driver. open up your box and take a look at the card, if it's a onboard card then less /proc/ioports, do that in a terminal go to ctrl+alt+F1, log in and then type that in.
that should show you what chip your card is using, hopefully it's not an isa card, if so then change the last input to less /proc/isapnp
then jump on google and find the card that you have. take a look at the amount of memory that it has, and the specs for it, right them down.
now go into the mdk control panel, bottom of screen, kicker(start menu), configuration, mandrake control center. once there then take a look at the hardware section, you should be able to configure the graphics card from their.
hopefully that helps you out some. welcome to linux, you'll probably be better at this than most of us, you have learned the blessings of patience over the years.