If it's any help, here's how I resize for Alamy;
1. I always shoot stock in RAW and edit in Photoshop (I use CS4).
2. In photoshop on 'Image' menu, make sure you are in 16 bit colour first of all, and then click 'image size'.
3. In the dialog box make sure all 3 boxes at the bottom are ticked and that 'Bicubic Smoother' is selected.
4. Set the resolution to 300 pixels per inch.
5. Make sure the longest side (height or width) is set to about 5000 pixels. The aim is to get the pixels dimensions figure at the top to 96mb or above, but as close to 96 as you can.
6. Now in the 'Image ' menu again, select 'Mode' and convert to 8 bits. This will halve the file size to about 48mb.
7. Now, save as a JPEG. The main thing is now Alamy can convert it back toa 96mb TIFF for the customer.
Hope this all helps. It works for me.