For a specific auction, I want buyers to be sent special instructions.
If this is not possible through Ebay, what is the absolutely easiest
way of doing this? I do have access to a PHP server, MySQL database,
and can program a bit in both. (I use PHPwebhosting.com) Unfortunately
I have no idea if or how I can read a webpage using my server, or
whether it is even necessary. I don't expect anyone to write any code
if its necessary to do so, only to guide me on how I should go about
this and maybe toss a few helpful one-liner sample codes.

Is it a single buyer for one item or multiple buyers?  You could set
up an email account that autosends the instructions to the email
adress of the buyer from the email that ebay will send you.  That
would require a little coding, but the concept is simple.

Or if the instructions are not that private, just make a link?

There will be multiple buyers for the item. It sounds like there would
be quite a bit of coding involved. I guess I could use a VB email
plugin of some sort... is that what you mean?

The instructions are private, and even if they weren't, currently I
don't post my address and also have to fudge my email a bit for
anti-spam purposes. It sure would be nice to just say "Payment address
& Paypal address will be sent to you automatically after end of
auction end."