should be able to directly connect the tape to your
soundcard,
provided is has line-level inputs (most cards do). Personally I just
connected my computer to the monitoring Tape2 input/output of my hifi
amplifier, so I can also record from a vinyl record player if I want
to. (You cannot directly connect a record player to most soundcards
because of RIAA distortion, you need a real phono input.)
Actually, to use a phono level signal into regular line inputs you can
use a matching transformer or a preamp
The problem with records is not levels, but the RIAA distortion. You
need a device which can adapt to this. There are special preamps for
this, some cards like the Terratec Phase26 USB has them built in,
normaly hifi amps have them (the input labeled "PHONO" most of the
time), but most soundcards do not have them.
Jan Depner has made a JAMin config file that undoes the RIAA curve, its
shipped with the latest tarball IIRC.