I embedded a Lightroom-generated Postcard Viewer gallery in our home page:
http://www.scphotographic.com
Now you want to know how I did it, don't you? It was a lot of experimenting, and it's probably going against a bunch of html rules, but it seems to work OK. Most of the fiddling was to get it to sit between the header and the footer.
I'm on LR 2.1/Dreamweaver MX2''4, reasonably dreamweaver competent, but no html genius, so I can't vouch for the acceptability of what I did in terms of protocol; it was all achieved pretty much by trial and error.
Our site, as you will see, is pretty straightforward, with a header, a footer, and simple content between. It uses local css.
Backup your entire site and work only on a second copy. This way when it doesn't work out you can revert to what was working before

Generate your gallery in LR, and 'Export' (rather than 'Upload') at the bottom of the RH panel and save it somewhere convenient.
Open the index.html file from the gallery. Open the index.html from your own site.
Cut and paste the bit from the LR index.html which does the business, ie (in my case) the bit starting <div id="flashcontent"> down to its closing </div>. Paste it after the closing </div> of the header in your index.html file.
Copy the other files from the folder where LR created its index.html and paste them into the folder where your website index.html resides.
Copy the images folder from the LR folder and paste it into your site - but be careful, because you may have an existing images folder, which has all of your images for your site. If so, rename the LR Images folder to eg LRImages before you copy it. If you do this, you will have to edit the references in your gallery.xml (which you copied from LR to your site) file to point to the new folder.
Go back to your LR index.html and scroll to the top. Find the line which starts <script type= and ends with </script>. copy it and paste it into you own index.html at the same place inside the <head> tag.
You will also have to cut/paste the appropriate bit inside the <style type="text/css"> tag. I just copied the whole tag and pasted it, so I now have two of these in my index.html file - I don't know if maybe I should have amalgamated them, but it works.
I also have a div#flashcontent in the original (my site) <style type="text/css"> tag, which I think I wrote from scratch. Likewise, below @media screen I have a * html div#flashcontent statement, which again I think I wrote from scratch.
Now all you have to do is spend lots of time fiddling with margins, padding and positioning until it looks right!
By the way, the text on our site above the postcards is an extra table I added inside the <div id="content"> tag, before the <div id="flashcontent"> (which is nested inside <div id="content">).
I hope this makes sense. Depending on which flash gallery you use, there may be some differences - I've only tried this one.
I hope I haven't misssed anything!
Best of luck. In the worst case, you can always go back to your saved copy!
Patrick Cunningham