I am building a new PC and would like to know what Modem and Sound card are supported by Mandrake 8.1, and is easy to install and or configure. Thanks.

any type of hardware modem or external modem will work.. with sound, usually soundblasters don't have any problems working under linux...

Would a USB modem and a Soundblaster 16 PCI card work?

as linux kernel 2.2.17 and later support USB, i would stay clear of a USB modem for the time being, most likely it will be hard to get working as there aren't many drivers for USB for Linux as there are in Windows environment.
the soundblaster you shouldn't have any trouble with, but i would try to go a different course for your modem... either external via serial/com port or internal hardware non-winmodem will do fine.

I have just installed Mandrake 8.1 on my PC and it is currently dual booting with Win98.

I found that Mandrake 8.1 works fine with my internal ISA US Robotics (3Com) Sportster Fax Modem. The modem is configured by jumpers for COM 2 / IRQ3 rather than being left in "plug and play mode" which never worked under Win98 anyway! Hope this helps if you are looking for an internal modem. The only problem is that very few high performance motherboards have ISA slots. I recently bought a Gigabyte 71XE4 Slot A M/B which has 2 ISA slots but this is unusual. I don't know of any other decent M/B's that offer this facility.

Alan

If your gonna get a new sound card, then get a Sound Blaster Live! 5.1 OEM its $32 bux at newegg and works great with crystal clear audio.

SB 16 is old news...

dont know if this will help,
but i dual boot with xp pro and mandrake 8.1, i have an external 56k modem(hayes accura ) and my sound card is a sonicfury(santa cruz). gametheater xp and hercules fortissimo should also work as they all share the same dsp (crystal fusion).

card is detected automatically no probs (doesnt like the bios set for plug and play os) apart from that its good.
midi isnt supported with the current drivers tho.