Most turntables output is too low to connect directly to your line-in. You have to go through a preamp or receiver. Connect the turntable to the phono inputs of the preamp or receiver and then connect the tape outputs of the preamp or receiver to your line in on your soundcard.
Download
Cool Edit 2000 and use that to record the LP's to .wav files. You can use Cool Edit to clean up any clicks, pops, and background noise, and split the LP into individual tracks. Note that 1 minute of 16 bit/44.1 kHz .wav audio takes up about 10 megabytes of hard disk space. And you need twice as much free space as the files take up to edit them. So a 5-minute song takes up about 50 megabytes of disk space, plus you need an additional minimum of 50 megabytes free to edit it.
Then use
CDEX and LAME to convert the finished .wav files to .mp3's