You need more than a phono pre amp or mixer w/ phono input. This pre amp or mixer also needs to have a digital out (usb or friewire) to send the signal to your computer. I think this was assumed in the post by "ksandvik", but I figured I'd point it out. He pointed out software, which you will need.
FWIW, I grabbed one of these (
http://www.alesis.com/io26) to record my band, and it happened to have phono inputs, so I have done a bunch of vinyl transfers with it as well. You should be able to get one cheap - I got mine brand new from Musicians Friend or Sweetwater (dont remember) for 200 bucks shipped.
It's a nice little interface, with 8 mic pres with inserts (can record 8 channels at the same time), 48v phantom power, firewire, Cubase LE bundled w/ it, you can chain several together via Lightpipe, and...the phono input.
In other words, you could get a lot done with it in addition to recording LPs.
