To narrow it down again (and reiterate what everyone else said):
If you want menus/options/etc from your iso's then I would say get a boxee or wdlive and keep your content as-is. (wd live will be cheaper, I think). Spare laptop, or bought cheaply is another excellent solution ($100-150). You can convert vga to hdmi pretty cheaply as well ($30) if there isn't a tv out, and now you won't have to do anything kludgy to get things working, plus now you can get all the web content in the world (especially if you add a wireless keyboard/mouse via usb). You can even load free software that won't make it look like a computer and it will be pretty slick.
However, if you are up to converting to save space/add more titles and have movies-only, then maybe roku will be enough. Several media server/channels out there ($15 roughly for lifetime). I know people with their high-def content must convert to mp4 otherwise they'd be constantly adding more drives to their system
Most people just want the film from the isos, so they are also happy with just that. You can set the batch up at night, do five a night and be done rather quickly.
And here is the opinion nobody asked for - I would be devistated if I lost all of those isos - I hope you have backups...