Can you tell us what version of Mandrake?
My last version with Mandrake didn't work with my asus onboard sound, but Mandy 10 plays nicely with it.
As for the modem, as it a winmodem? If so you'll need some drivers for Linux to talk to the modem. Check out www.linmodems.org to see if a driver for that modem is listed.
As for the graphics card, ATI's are a pain to get working. Try running XFdrake as root, try selecting the stock drivers and see if they work. If not, you can try the ati linux driver from their site. You can download it from windows and access it from within Mandrake.