Hi -- I'm wondering if I put something on one page if I can have that exact same thing appear across all the pages.

For instance, if I have a website with 50 pages and decide to add a new logo in the top right corner, is there some way I can have that logo appear on all pages without having to copy and paste to each? Thanks

Please don't shoot the messenger, but unless you are starting from scratch the anser is NO

(1) new website created from homepage design, select home page as template on every new page you set up, and delete out what you don't want on the new page, and your logo etc will be there.

(2) website already created, change logo on every page individually

(3) made lots of changes on lots of pages select all elements whilst holding down shift key, and then paste on every page.

Sounds daft, but actually it has advantages especially for SEO that its done this way

(4) only have one home page and and your website content in an iframe for every other page, useless for SEO and i believe complicated to set up

Here's another way.
When you create your image name it logo.jpg and add it to your pages.
Now if you want to change it on all pages later make the edits to it and save it back to the same location and name it was when you added it to your page. Now VSD should see it was changed and update the pages. Keep in mind that it should have the same dimensions as it did before to keep things correct.

Hm. Interesting idea. I'm still in the process of building a new site, so I'm just trying to foresee any issues. Especially since it's going to be a web comic which will obviously result in a lot of pages, I wanted to make sure I was working with the best possible foresight.

Perhaps the best solution would be to create the bulk of the page as a single image in PS and simply have all of the buttons be layered images on top of that.

I made my own single image backdrop for the wedding site http://www.chauffeurdrivenluxurycars.co.uk/index.html

I actually built it with VSD then previewed it, saved for web to optimise and put it in as a background image

There's several ways to accomplish this. If your server will sparse php in an html page that's another solution. Iframes come to mind also. Javascript includes is another one.