A decent turntable. Very easy to find at thrift stores or garage sales now that all is CD and Ipod. Anywhere from $2 and up. Mine was $2 for a JVC and stylus. It's a bit of a crap shoot as this one works better than the $24 I spent on a turntable at the Salvation Army, plus the $37 for a new stylus.
An amplifier Most turntables don't put out enough power to connect directly to your computer. You'll need an amplifier to boost the signal. This is a $5 (garage sale)mixing board from Radio Shack, but you could use any decent amp. Again, easy to pick up at a garage sale. The one weak point of amplifiers is the capacitors which can fail after a few years and lead to a lot of added noise or a channel dropping out. This is usually why old stereos crap out on you.
A decent audio editor. Audacity. is a free sound editor you can use to record, edit and convert sounds to MP3 files. I use an older version of Sound Forge which also allows for automatic click and crackle removal.
It takes about an hour and a half to convert an album including recording, breaking a sound file up into tracks and converting to MP3. The quality is pretty good, but it really depends on the state of the record, turntable, amp and sound card.
I've been converting some nice old Vancouver 80's punk there's no way I'd ever find on Itunes. It's fun to listen to DOA, Pointed Sticks and Poisoned again. Of course, given these albums are 20 years old and still playable, and I've yet to meet a computer file format that's lasted that long - I may just be spinning some wheels here.