I’m setting up Monoslideshow for a client who wants to add/remove images from it via the Gallery module. How would you go about setting it up so the client can add and remove images to it as they like? For instance, there might be 100 photos in the gallery but they only want to display 8 in the slideshow and they might want to add and remove ones at a later date?

Let me start off by saying that I’ve not used Monoslideshow before.  I use SlideShowPro for all of my Flash slideshow needs.  But, from a google browse of their website, it looks like your typical XML-powered Flash slideshow.

In that instance, I actually wouldn’t use the Gallery module.  Are you using the gallery module for other parts of the site?  Are the images reused in other places?  If so, the below might not be the best option. 

What I would do is set up a weblog, where each entry would be an image.  Then, create a XML template to format the XML as needed (whatever the format for Monoslideshow is).  Your client could upload more images as needed and set the open/close status as needed.

Yes, they will be using the gallery elsewhere which was why I was hoping to be able to implement both the gallery (using Lightbox) and the slideshow from the same interface.

I was just looking at this in the wiki - http://expressionengine.com/wiki/Gallery_Relationships/

It might be possible to somehow use a relationship if you were able to select multiple gallery entries to attach to a particular post, and then use that single weblog entry to populate the XML file rather than directly from the gallery. Can you select multiple entries using relationships though?