What is the best way to make MP3s for playback on my RioCar from my album(vinyl) collection?

Purchase them on CD.

I'm serious.

Remember that CDs have greater potential dynamic range and frequency response than LPs. Back when LPs were made, they knew the limitations of the playback equipment, and the LPs were mastered with those limitations in mind. So LPs are EQ'd and compressed a lot worse than a CD would be. An album that's been remastered specifically for CD will usually sound significantly better.

Also keep in mind that when a record company remasters an old recording for a CD, they are using the original master tapes going straight into a digital system at a multimillion dollar mastering facility. So there is much more direct sound reproduction without the pops, wow/flutter, overdrive distortion, level problems, etc., that you're going to run into when trying to grab an LP with your cheap $20.00 sound card. Not only that, but the mastering engineer doing the job is a professional who knows what he's doing and has many years of experience at it. You, on the other hand, had to ask on a BBS how to plug a record player into a computer.

Weren't you the guy worried about the quality level of your MP3s? Surely you know the concept of garbage-in-garbage-out. You try to run your beloved LPs through a cheap PC sound card and you're not going to be happy with the results.

Note: Above discussion is moot when referring to an LP that isn't available in CD form. In this case, you can attempt soundcard sampling, but it's going to take a learning curve on your part before you can start to get something that sounds like what you want it to sound like.