Using 2 Or More Servers For 1 Site

I've just initiated myself to splitting the load between servers... in this case, one server delivers all the html/php/mysql/emails, another serves all the images... its an auction site so there are loads of images.

Just did some testing using Firebug, with 20 5-10kb thumbnails loaded from the image server, everything else from the original server... the results speak for themselves:

no browse cache:
current - 11.7 seconds
test - 5.6 seconds

refresh (checks modified date on some/all files I believe):
current - 8.6 seconds
test - 4.1 seconds

I'm not testing scientifically or anything but these times were fairly consistent over a few dozen trials. Obviously also there are other factors with network connections, server loads etc. From my primitive knowledge I figure that if you fork the requests down 2 or more paths, instead of just 1, then you are virtually doubling the amount of requests that are taking place, hence the page loads faster.

Is this consistent with what others have found? In this case I figure the images are the common denominator so having them on the 2nd server makes sense. I also understand that databases, emailing and other processes can be split onto a separate server...

On a final note, can I get a recommendation...

#server 1:
hosts html, css, javascript, PHP, MySQL databases, and sends emails... php 5 is required and security is very important

#server 2:
hosts images and will possibly stream videos... basically just a file system we can access from another site

What would be the advisable server specs and operating systems for each? They would not be under a heavy load for some time, but the idea is that they could be further expanded if necessary. I understand that lighthttpd is good for serving images?

and finally, I also require:
- a good host
- a backup solution

if anyone could recommend anything to me at this point that would be great!

P.S. don't worry, i'm not setting the servers up myself - but i'm kindof in the position where I have to make the decisions!

Off Topic:
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