When you download images, select two checkboxes - one for localhost and one for your ir 150. That'll make the images available when proofing on your local machine, and also make the images available on the ir 150 so you can take advantage of printer centric mode when printing.
One of our RIPs is only available via a "hold" queue. The image downloads would appear as jobs labeled "unknown". The operator just needs to print those jobs. When he hits print, the PostScript code required to store the image on the hard drive is executed, no output is generated and the image contained in that job is now available on the printer's hard disk. I mention that just in case you have a similar situation.
RIPs I've used in the past often have an option to print a list of resources on the printer's hard disk (including your images/forms). If that's not an option, I'm sure there's a bit of PostScript code laying around somewhere that will print out a list of internal resources. If you're using a stand alone RIP instead of the built-in RIP, you can just browse to the folder where images are stored and look over the files stored there.
Jim