I'm going to agree and disagree with Theun. First of all, yes, doing the downsampling in Photoshop first is a good idea. However, it's not true that it doesn't matter whether it's done in Photoshop vs. InDesign! You can get a much better quality in Photoshop because ID's downsampling (at print or pdf-export time) is very limited and not very smart. In Pshop, you can use Bicubic Sharper (in the image size dialog box) for a better quality downsample. Or you can use bicubic and then manually work with Unsharp Masking or some other sharpening technique (takes longer, but more control).
I also disagree that JPEG is so bad. I agree that it should be avoided if you're going to keep editing the file (because you want to avoid repeated compressions), but if you're just opening, resizing, sharpening, saving, and importing into InDesign, then JPEG (with high quality/low compression) is a very good option. Yes, it degrades the image, but only a very small amount. At maximum quality, virtually no one would be able to tell (if it's a photograph from a digital camera).
