Running Windows 7. Can I connect cassette player to my PC using a USB port rather than Line In?
Sure, if your cassette player has a USB port. 
Make sure to select the USB device as your recording device in Audacity.
…Lots of people seem to have trouble with those “cheap little” USB cassette players. I’m sure most of them work but of course they are very cheaply made.
Thanks DVDdoug. The cassette player is a Sony with a mini jack earphone socket as output
If you have a desktop/tower computer with a regular soundcard you can connect headphone-out to line-in (blue). A headphone signal is about the same voltage as a line-level signal, depending on the volume control setting. A headphone ouput is just capable of driving a lower impedance load, plus there is always a headphone volume control.
The microphone input on a laptop is “wrong”.
If you have a laptop with no line-in you can get a USB interface with line-inputs. The Berhinger UCA202 (or UCA222) is popular and inexpensive. Note that it has RCA input connections so you’ll need a different cable. Do NOT buy a regular “USB soundcard” because they are like laptops with only line-in and headphone
Thanks again. I’ll do headphone out to line in. Am sure it will work. It’s just that I had a headphone out to USB cable handy.
It’s just that I had a headphone out to USB cable handy.
OK, that should will work. But it can’t be" just a cable" (if it works) . It’s a USB interface (an analog-to-digital converter inside, etc.). The electronics can be small so it might look like just a cable.
You can try it both ways to see if one works better than the other. The only noticeable difference should be noise. If one is noisier then the other you can use whichever has lower noise. But the analog tape noise will probably dominate anyway.