My computer spec sheet says I have a 56K, V.90 modem. But how can I find out what kind I have. My manufacturer went out of business so I can't ask them. My modem is performing really slowly so I want to look it up on the web to see if I can do something.

If you want the name of the modem,go to device manager. see the name there.

it should give some information in device manager go to control panel, select sytem,a
sysyem properties box will popup select the device manager tab look for your modem there
for more info go to windrivers.com they have a modem search there quite usefull

All modern electronic devices have an FCC identification number on them. The FCC got involved to insure compliance to standards regarding interference among TV, radio and other signals. On the web (http://www.fcc.gov/oet/fccid/) you can look up any PC card, by the number, and it will give at least the manufacturer. They even have a handy guide to drivers and links to driver sites!
Don't believe the Windows designations, but you might note them. Someone just tried those drivers and they sort-of-worked.
On the bad side, if the manufacturer has completely gone out of business, you are probably going to have limited options.