Aperture will use one or the other of the files as your Master (you choose which), but even if you choose the RAW as your Master, Aperture will generate a preview of the image which it displays in the library. If you truely want to look at the jpeg and the RAW, you would probably want to set the Master as your RAW file. Then, using export from the File menu, you can export the Master (RAW) and a version (JPEG). Open them in Preview and you can look at them side by side.
Anyone think of a better way to look at the RAW and JPEG next to one another?
As always, start by copying the images on to a folder on the hard drive and then backing up the folder. Never import directly from camera or card into Aperture or any other images app.
Then since this is an exercise not a batch workflow, simply rename the RAW and JPEG versions of one image and separately import each renamed version into Aperture. The two should each be Masters, one from the JPEG original and one from the RAW original.
Note the JPEG may initially "look" better on the (relatively low resolution) display due to in-camera presets like sharpening, etc. not present in the RAW file. However the RAW file contains much more image data, is much more editable and is capable of making superior (relatively very high resolution) hard copy prints.