Yeah CaptSkip will take great care of the tapes, he did a lot of remasters of really noisy ABB tapes and always does a great job. No worries there, but it is a very good idea to make a copy yourself just in case.
Make sure you copy the tapes to digital as a .Wav file at at least 44.1khz sample rate, 16 bit bit depth (CD quality). This day in age there is much more clearer bit depths with more "depth" available in the sound but if its a crude tape there won't be much more sound to capture, but you could go 24 bit/48khz or even 96 khz if you wanted a very pristine copy.
Just make sure you don't use a little line out of the tape machine into the "mic" input on your computer, that will introduce clock/line noise from the computers processor and the hard drive spinning and such. A USB converter like you're saying is good, or a very high quality sound card. You probably don't need to go crazy if this is your only tape, but if you have lots of rare tapes you may want to invest in something nice.
