I would like to sample audio from popular songs to remix - is this possible within Reason 5 or Record 1.5?
It certainly is possible in Record, but in Reason too, although dreadful. Nonetheless, I will explain the procedure in Reason: First you will have to export material you are working on into .wav/.aif clips. Then the clips have to be loaded into either Redrum or NN-XT. The actual remixing process is theoretically simple, simply trigger the audio clips in the playlist normally (and remix to your hearts will).
There are few advantages of doing this over other DAWs. Most of the time you will not be able to fast forward, because Reason doesn't directly support audio clips in playlist like other DAWs such as FL Studio or Cubase do. It simply triggers the sample once and plays it from start to finish (if not interrupted), and that's it. And because of the lack of support for audio clips in playlist you have little visual feedback about what you are doing. You can't simply see when a clip ends, you have to know it. But, if the audio clips you will be using are less than say, 5 seconds long, these might not be issues at all for you.
Record deals with all the disadvantages I've mentioned, and is a much saner DAW to use when using longer audio clips.